My old coworker is weirdly nice

I’m a very anti social person, unless I’m at work or with friends. My old coworker goes to the same college as me and he always says hi whenever he sees me. He’s a very friendly guy haha. He’s always the first to wave or say something and it just makes my brain go “wtf?” Lol we never talked much at work either so that’s why I think it’s weird haha I personally just think it’s kinda strange, because we haven’t worked together since July, and just today I saw him and he said hi.

I’m adding to this group cause I saw “relationships” and I’m not sure where else to go