"I'm curious, how do you know that he's using muscular force only?"
I'd hazard a guess that it's because he says "force this this way", or "You have to pull this around", etc. Or just that he can be seen to be forcing things, perhaps. But then, I'm not there, so I'm just guessing. Jop?
"Moreso, does that mean that all the other students also use muscular force?"
Not by necessity, but surely it means that they're more likely to, if that's the way that they're taught?