This is actually realistic, MC is a kid with powers, is like a new toy, he will use it an duse until he finds ways to play with it, and levelling up have no stop potential.
Now he is only interested in testing his limits, or making them bigger.
He was a new transferee, didn't knew anyone in class and he knows they are alive so he doesn't care, but for the whole country a explosion happened and 20-30 kids EVAPORATED, of course people want to ask the only "survivor" questions.
In a sense is good he is fainting from the tries as it makes it look like whatever happened had long lasting effects on his body, any curious journalist will simply come up with "misteryous explosion and survivor is chronically ill", but it akes his family worried because now they think he is deadly ill or brain damaged.
Wonder how is discovered MC have powers and countries want to kidnap him.