What does a squeeze on the shoulder mean?

Some people need to see and some need to touch. Don't think it means anything, it's probably the kind of thing he/she does to absolutely everyone.  See if he/she does it to other people. If not maybe there is something he/she is trying to tell you. It maybe a physical connection which some people find aids a conversation or a way of getting your attention (romantic way). He/she maybe totally into you! Good luck.

If it's something you don't like or approve of than tell he/she to please keep their hands to their self. It's not your type of thing. Good luck.

I would think of it as an expression of support or encouragement.