The difference is, that if the teacher was aware of what he was doing, he wouldn't do it. And if the child wasn't aware of what she was doing, she would behave the same way. If the teacher had a little neurofeedback button that somehow would light up when he was upset, or rationalizing, being impulsive, or otherwise cuing him when he was not thinking the way he would like to think, his behavior would change (somewhat).

It's the difference between saying that someone with autism doesn't care about people vs. someone saying with autism cannot understand how other people are feeling, or saying someone with ADHD is lazy vs. they desperately want to work but can't control attention, or saying someone with face-blindness just doesn't care about faces. (That's what someone without those disorders would think first, since the behavior that the disordered person exhibits matches what they would do if they didn't care).

motivation and intention do not have to be the same at all

I agree, they don't have to be the same. I'm making the case that small instances of real difference, coupled with poor modeling of other people, enhances and exaggerates the perception that they are not the same, and that for smart people this is particularly bad because everyone around them is just kinda globally worse off on every dimension...and because of typical-mind fallacy the smart person will then assume everyone's just kinda alien and terrible in their intentions rather than just slightly worse at carrying intentions out.

When I'm dealing with someone I know well who is "normal' and I see behavior 6 happening in a situation where I would have done 2+3= behavior 5, I model the other person as accidentally doing 2x3=6. Under typical mind fallacy, I would assume that they had similar minds (2+3) but different behavior (5) and conclude that those people just don't care about equal signs I am so very alone and that's the trap to avoid.