For an induction machine to operate, you must be able to generate a rotating field on both the rotor and stator. The fields couple through the air gap, giving you power transmission through torque and speed. The machine cares less about the direction of power travel than you'd expect!
The connections from Simscape set up both voltage and current constraints for the underlying electrical net. The machine itself appears to the network essentially as a grouping of inductors and speed-dependent source terms. So by connecting the speed, torque, and electrical terminals, Simscape is constructing a circuit network where it simultaneously solves for all the voltages and currents that make a consistent operating point and satisfy the power/speed inputs, too. If it helps, you can think of Simscape networks operating a little more like SPICE than an explicit ODE solver.
Contrast this with a purely Simulink driven system, where you'd generally begin by formulating the machine equations to solve for the output of the flux linkage differential equations in dynamic operation. The ODEs would still have source inputs of voltages, but there could be a feedback network with a load on the stator output that responds to current flow with the induced voltage on the stator side. In that way you would still be supplying the stator network with the terminal voltages. For steady-state operation, you can remove the terms and solve the characteristic equations for the voltages/currents/speeds/torques/etc explicitly from either voltages or currents or a combination of them. If you take the simulink-only approach it is often easier and more numerically advantageous to solve for the system in the rotating (qd) reference frame instead of abc variables.
Hope this helps!