I would suggest reading the text file as text, extract the header, and then parse the data with tools like textscan.
(You can get my readfile function from the FEX. If you are using R2017a or later, you can also get it through the AddOn-manager.)
URL='https://www.mathworks.com/matlabcentral/answers/uploaded_files/867210/sample%20test%20data.txt';
try data=cellstr(readlines(URL));
catch, data=readfile(URL);
end
%make use of the fact that this is solid block of text
data=cell2mat(data);
loc=find(data(:,1)=='#');
header=data(loc,:)
header = '# SeqNum ChN Pri Srv MC PowerA PowerB NoiseA NoiseB Time Stamp (s) Dest MAC Addr Src MAC Addr EthTyp Mat Errs Leng '
data(loc,:)=[]
data = 39×137 char array
'1611574502 184 000 001 10 -73.0 -80.0 -106.0 -104.0 00000000006346.226848 33:33:00:00:00:fb ea:99:0e:0a:53:f7 0x86dd Yes 0086 0097 '
'1170211136 184 006 001 10 -73.0 -75.0 -103.0 -104.0 00000000006346.590584 ff:ff:ff:ff:ff:ff ea:99:0e:0a:53:f7 0x0800 Yes 0085 0324 '
'0000000017 184 004 001 11 -99.0 -98.0 -103.0 -107.0 00000000006361.062418 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'1611574502 184 000 001 10 -68.0 -67.0 -103.0 -107.0 00000000006362.239553 33:33:00:00:00:fb ea:99:0e:0a:53:f7 0x86dd Yes 0086 0097 '
'0000000019 184 004 001 11 -101.0 -98.0 -103.0 -104.0 00000000006363.062618 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'1170211136 184 006 001 10 -67.0 -66.0 -106.0 -104.0 00000000006363.169210 ff:ff:ff:ff:ff:ff ea:99:0e:0a:53:f7 0x0800 Yes 0085 0324 '
'0000000020 184 004 001 11 -99.0 -96.0 -103.0 -104.0 00000000006364.062714 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000021 184 004 001 11 -99.0 -96.0 -103.0 -104.0 00000000006365.062836 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000022 184 004 001 11 -99.0 -98.0 -106.0 -104.0 00000000006366.062957 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000025 184 004 001 11 -99.0 -97.0 -103.0 -104.0 00000000006369.063322 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000026 184 004 001 11 -100.0 -98.0 -103.0 -104.0 00000000006370.061493 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000027 184 004 001 11 -103.0 -98.0 -106.0 -107.0 00000000006371.060627 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000028 184 004 001 11 -98.0 -96.0 -106.0 -104.0 00000000006372.060709 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000029 184 004 001 11 -98.0 -95.0 -106.0 -104.0 00000000006373.062754 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000030 184 004 001 11 -97.0 -99.0 -106.0 -107.0 00000000006374.061901 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'0000000031 184 004 001 11 -99.0 -101.0 -106.0 -104.0 00000000006375.060098 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'1610612736 184 000 001 10 -66.0 -68.0 -103.0 -104.0 00000000006376.092635 33:33:00:00:00:16 ea:99:0e:0a:53:f7 0x86dd Yes 0090 0100 '
'1170211136 184 006 001 10 -68.0 -69.0 -106.0 -104.0 00000000006376.167784 ff:ff:ff:ff:ff:ff ea:99:0e:0a:53:f7 0x0800 Yes 0085 0324 '
'1610612736 184 000 001 10 -68.0 -68.0 -103.0 -104.0 00000000006376.176339 33:33:00:00:00:16 ea:99:0e:0a:53:f7 0x86dd Yes 0090 0100 '
'1610612736 184 000 001 10 -66.0 -67.0 -103.0 -110.0 00000000006376.292866 33:33:00:00:00:16 ea:99:0e:0a:53:f7 0x86dd Yes 0090 0100 '
'1610612736 184 000 001 10 -65.0 -68.0 -103.0 -104.0 00000000006376.335958 33:33:ff:86:c6:88 ea:99:0e:0a:53:f7 0x86dd Yes 0066 0076 '
'0000000033 184 004 001 11 -97.0 -97.0 -103.0 -101.0 00000000006377.063311 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'1610612736 184 000 001 10 -65.0 -65.0 -106.0 -104.0 00000000006377.362680 33:33:00:00:00:16 ea:99:0e:0a:53:f7 0x86dd Yes 0090 0100 '
'1610612736 184 000 001 10 -64.0 -65.0 -103.0 -107.0 00000000006377.371204 33:33:00:00:00:16 ea:99:0e:0a:53:f7 0x86dd Yes 0090 0100 '
'1610612736 184 000 001 10 -63.0 -65.0 -106.0 -104.0 00000000006377.456220 33:33:00:00:00:16 ea:99:0e:0a:53:f7 0x86dd Yes 0090 0100 '
'1610612736 184 000 001 10 -65.0 -64.0 -103.0 -107.0 00000000006377.524713 33:33:00:00:00:16 ea:99:0e:0a:53:f7 0x86dd Yes 0090 0100 '
'1611381948 184 000 001 10 -64.0 -68.0 -106.0 -104.0 00000000006378.050636 33:33:00:00:00:02 ea:99:0e:0a:53:f7 0x86dd Yes 0042 0052 '
'0000000034 184 004 001 11 -96.0 -98.0 -106.0 -107.0 00000000006378.062425 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'1611574502 184 000 001 10 -64.0 -69.0 -106.0 -107.0 00000000006378.086883 33:33:00:00:00:fb ea:99:0e:0a:53:f7 0x86dd Yes 0187 0198 '
'1170211136 184 006 001 10 -65.0 -67.0 -106.0 -104.0 00000000006378.372313 ff:ff:ff:ff:ff:ff ea:99:0e:0a:53:f7 0x0800 Yes 0085 0324 '
'1611574502 184 000 001 10 -65.0 -66.0 -106.0 -104.0 00000000006379.268748 33:33:00:00:00:fb ea:99:0e:0a:53:f7 0x86dd Yes 0086 0097 '
'0000000036 184 004 001 11 -97.0 -101.0 -106.0 -107.0 00000000006380.061666 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'1611574502 184 000 001 10 -63.0 -67.0 -103.0 -104.0 00000000006380.171144 33:33:00:00:00:fb ea:99:0e:0a:53:f7 0x86dd Yes 0187 0198 '
'1611381948 184 000 001 10 -62.0 -66.0 -106.0 -104.0 00000000006382.051341 33:33:00:00:00:02 ea:99:0e:0a:53:f7 0x86dd Yes 0042 0052 '
'1170211136 184 006 001 10 -63.0 -69.0 -103.0 -104.0 00000000006382.867419 ff:ff:ff:ff:ff:ff ea:99:0e:0a:53:f7 0x0800 Yes 0085 0324 '
'0000000039 184 004 001 11 -96.0 -100.0 -103.0 -104.0 00000000006383.060977 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '
'1611574502 184 000 001 10 -63.0 -67.0 -103.0 -107.0 00000000006383.269347 33:33:00:00:00:fb ea:99:0e:0a:53:f7 0x86dd Yes 0086 0097 '
'1611381948 184 000 001 10 -66.0 -64.0 -106.0 -104.0 00000000006386.049936 33:33:00:00:00:02 ea:99:0e:0a:53:f7 0x86dd Yes 0042 0052 '
'0000000043 184 004 001 11 -99.0 -97.0 -103.0 -107.0 00000000006387.067579 ff:ff:ff:ff:ff:ff 04:e5:48:00:10:00 0x0000 Yes 0000 0104 '