So... I don't understand.
Why does he care? Are they dead in front of his house, or some other minor inconvenience?
Because this dipshit thinks that people are "stupid" simply because they speak to him, amd utterly doesn't give a single shit about anything but himself.
I mean, he is so pathetic that he doesn't even realize the world around him exists as a thing other than for his own use and convenience.
His brain is, like... an exceptionally spoiled 3-year-old; why does he care what happened to things that he doesn't even recognize as "people?"
He shows, time and again, that he has no awareness of other people existing as fully formed beings, and constantly displays a crippled and mutilated psyche towards the existence of others, so there's no real reason for him to experience any form of emotion regarding the death of a classmate, or even a fellow human, any more than he would a fly or a flower.
Certainly, not enough to clench his fist!
Either that, or the mangaka is a fucktard who has no ability to write... or the writer is a pathetic child.
Either way, his reaction makes no sense.