Shigaraki prefers to do his training where no one can bother him and use the library to read up on more things to do with his magic type. It was his one trump card that he had where it came to having one over the brats that thought threatening him about what he could or couldn't do. The last thing he was going to do was let them figure out how to counter it.

But, having interest in seeing what was available in these places where he could still keep that coveted secret lead him to watching this poor sap get owned by his own attempt. Even without the dynamite or attempts at forming both magic and the choice weapon together, Shigaraki recognized just who it was.

"Because you're the wrong kind of angry." Simple and easy. Ask the most angry man in the entire world.