ADVICE: 13yo struggling with friend drama at middle school

So my oldest just started middle school and apparently had a falling out with his best friend from elementary over something stupid (choosing different lunch table groups?? still not entirely clear). He's in his room, won't talk about it, and I'm getting the silent treatment when I try to ask. I remember middle school being rough but I also don't want to completely dismiss what he's going through. Do I push to talk about it or give him space? How much of this is normal and when should I actually be worried? He's usually pretty social so this is unlike him.