There are a lot of cultures where seating in public is ad hoc, you just sit wherever, you generally don't claim a table or area to yourself. In those situations greetings and socialization are pretty normal.
I remember going out to eat fast food with a girl and her kid a decade ago and some homeless guy asked if he could sit with us. I said sure, and he was a nice maybe 50 year old guy. He had clearly been around kids and enjoyed the normalcy of just hanging out with the three of us for 30min. The kid didn't mind, but the girl I was dating thought it really weird.
Didn't that guy get shot in the face?