Perhaps he didn't want you to feel that he was invading your space, or was busy thinking of the next session, or switching off for a few minutes. Primary or secondary? Why don't most of them know your name? Have you ever brought biscuits or cake in to break the ice? Are you involved in any way with planning or other activities in the school, rather than just teaching the class?
At a school today as a supply teacher where I ve taught regularly over the years. I am able to chat to staff members and say hello and on more of a hi, how are you basis with them. Don't think many of them know my name though.
But always treated like I have the plague in the staff room. No one smiles, no one sits next to you, one bloke went and sat on his own rather than sit by me.
That is the one thing I had about supply, having no friends.