First Grader left alone in cafeteria?

I don't know if I'm overreacting about this or not and just need opinions. My seven year old son has ASD but is a part of a normal first grade class.I walk him into school every morning and to his assigned lunch table in the school's cafeteria. He eats breakfast at home but looovveesss the school's chocolate milk and drinks one every morning. I wait around so I can help him open the carton (We're working on him being able to do it himself.). I also hang around until I spot his teacher because of an incident with another student that happened earlier in the school year. Once I see her, a wave or a nod, me and my toddler leave.This morning we were running behind but made it inside just as the bell rang. The office clerk shuts the doors and anyone coming in after is tardy and has to buzz in.Well, we do our normal thing, most of his class is throwing away their breakfast and such but my son has already gone through the now empty line and gotten his milk. His teacher passes me and smiles and walks down the hall with most of the other kids following. I turn around and my son has sat down and started drinking his milk and I'm like "Buddy we need to get to class. Don't you have to line up or something?" He just shrugs.At this point the cafeteria is nearly empty. I kind of look around for direction since normally I'm gone at this point but I can't spot another adult. No one is at his table, and everyone is leaving. So we head towards his classroom at the back of the school building and teachers are closing their doors and the halls are emptying and I'm thinking "Does anyone even realize or care that my kid is just wandering around? What if I'd dropped him off from the car line?"We get about half way to his class and a teacher stops me and tells me that I need to check in at the office because I don't have a visitor sticker. I was kind of irritated but I get it. I wouldn't want some rando walking around the school, but I've got my seven year old and three year old with me. So I told her what's up and she just points the way to the office.I walk in there, and no one is at the desk but I hear the VP in the office. She gets me a sticker, the clerk shows up after. I ask the VP "So does my son always get left in the cafeteria alone?"She says "Oh he knows where to go after.""But there's no one in the cafteria. What if he decided he didn't?""Oh it's fine."She got busy, walked away, whatever. So I walk my son to his class. They've already shut the door and started so I don't want to walk in and disrupt things. My son does his thing (backpack hook) and walks in and me and my toddler leave.I just keep thinking though, how often is he left unsupervised and unaccounted for? I like his teacher and mostly like the school. They've offered a lot of therapy resources that have helped my son over the years but I question whether he's just being forgotten? What if something happened in the cafeteria and there just wasn't anyone around. What if I left him and he just walked out the door, would anyone have noticed? Am I being crazy for worrying about this?Tldr: First grader would have been left alone in the cafeteria if I wasn't there. Am I being overprotective? via /r/Parenting http://ift.tt/2izgceP