He ended up spreading his sickness to his classmates.
Did he spread it on purpose?
Yes, he did. He was proud of it.
If someone is sick they should stay home and not go to school. They especially shouldn't purposely try to get others sick.
He made them all sick on purpose because he's an asshole.
That is very rude behavior to try to get other people sick. You should talk to his parents about what he did so they can explain to him why what he did is wrong. It's extremely dangerous to try to get other people sick, especially with the current global pandemic.