He has that much PTSD from the shitty parenting he's been subjected to all this time that even something neutral is just another assault. Dude can't even start on the whole self-esteem thing (which he sorely needs) until he can clear the instinctive shell-shock response from his system.
Or someone can just forcibly bypass all that by marching in and straightforwardly dragging him out of all that bullcrap with an honest declaration of emotion, intent and resolve. Tiptoeing and nudging sure won't cut it.
Not sh*tty parenting. Because that implies that the parent is over all a bad parent. But rather, just too much pressure
This is more sh*tty communication....
But more the fact that he felt the pressure. He probably wasn't doing all that well when his mom was complaining or he was doing worse, so she just got mad.
But he probably took that to mean he wasn't good enough and had to do harder....
Mom's intention was probably only for him to try his best....
But she didn't bring that out well so for him, it was more him thinking he wasn't good enough...
So when he hears that his mom is happy with his score, what he's hearing is that he just isn't worth getting yelled at when she probably was happy that he was doing his best.