One of my ts didn't know that Christmas Tree lights get tangled, so I assume she has never dealt with that. So maybe she doesn't celebrate Christmas?

I think they might wish me Happy (pick your holiday), but to be honest I don't really care if they do or not. Random strangers wish Happy (pick your holiday) so I guess for me it doesn't mean anything other than polite conversation. If the holidays were hard for me, I would definitely talk about it in session. Or I might mention my plans if I was either excited or concerned about them.

I do think that if I didn't celebrate Christmas, I would not like being told Merry Christmas by my t. I would be hurt that they assumed I did celebrate. I would find it weird to be wished Happy Hanukkah but not offensive. Reflecting on all that, it may well be a conscious decision on the part of t to not say anything.