Because he's a nice person and wanted to be friendly. Why can't Skylar just say no to being friends without being an asshole? It was only the second time they interacted and he wanted to compliment his photos. I just don't think it's correct to call this introvert behavior or excuse it because he had past trauma. Some people just like talking and being nice. Skylar apparently knows how to be decent since he can be friendly with the teacher. Have respect for your peers too.
That is not an introvert thing. That's being an asshole. Nobody is being nice to you because they give a damn about you. It's just basic common decency.