It’s obvious that there’s a lot on his mind right now.
It’s obvious that he’s questioning a lot of things.
It’s obvious that he’s feeling a lot of conflicting emotions.
Yet, despite all that, he comes back to the main issue here and addresses it.
He composes himself and prioritises Nino’s feelings and problems here because Adrien knows that Nino can’t help him with his own and it’s what mattered in the moment.
He’s not prone to lashing out all the time and he’s not dangerous (he’s a kid!), contrary to some people believing that, because he broke a chimney.
He can compose himself, he does compose himself most of the time, he represses his emotions most of the time.
But not all the time. As he can only repress so much.
Especially when he’s told that he’s not needed in a very insensitive way (ofc no shade to Alya seeing how she was on a time limit), and after growing up with so many isolation and abandonment issues, thinking that the one position you wouldn’t feel left out in, makes you feel left out, and since you repress too much and never express your emotions, you have no outlets of expression and end up expressing it through breaking a chimney.