Todoroki is right that it upsets him. Katsuki hates being forced to look at himself. At his feelings. He needs to think a moment. Because vulnerability does not come easy to him.

But... Todoroki has him pegged. He's already figured him out. There is nowhere to hide and... he regrets ever texting him in the first place.

It's not the same at all.
You didn't treat him like shit your whole lives.
You don't still treat him like shit sometimes.