Most high school yearbooks hand out arbitrary titles like "funniest kid in class" or "most likely to be famous" and it usually doesn't mean much outside the very specific context of that school. However, there are the rare times when the teen elected "most likely to be famous" actually shoots into full stardom.
Regardless of how casual your interactions were, if you came up in school with someone famous, it's only natural that it will serve as happy hour gossip eventually. Even the most mundane of interactions can be used as fodder for speculation about whether a celebrity is a solid person or not. So, if you have multiple years of schooling with them that's a goldmine for analysis.