That brief mortified look gives Chara an equally brief 'cat surrounded by canary feathers' satisfaction before it goes and takes that with it, especially with what he says next. They prop their head on their hand.

"And that is my fault how? Shall I keep you updated with my whereabouts every second of the day?"

Not hecking likely, says their tone, and there being no phones here is not the strongest reason why. Normally they wouldn't put such a strong defense of their actions forward (they did physically attack first, theirself being an unthinking menace again), but their contrarian streak is raising it's head and joining forces with the fact they don't like him at all.