When you look at those audio examples, you will see that there is a phase of reading the data (such as calling audioreader()), and that once the data is in numeric form, that the example paid no further attention to the fact that the data came from an audio file.
So what you need to do is just whatever technique is appropriate to your eeg data in order to read the data as numeric form. Once you have done that, you can follow the rest of the example on how to do the stft and plot it using spectrogram(). spectrogram() does not care where you got the data.
Note: spectrogram() can only work on one channel of input at a time. It is not uncommon for EEG to be multiple channel.
