Another vote here for asking him about the chair.

My T recently scooted his chair back a couple of inches at the beginning of our session. I could tell it wasn't exactly in it's normal spot and he was moving it back. I just assumed that the client before me needed more closeness with him that day. I must have been either really distracted or in a REALLY good place at that moment, because normally that would have bothered me, but right then it didn't.

I can see where "thanks" would be kind of a disappointing response to the heartfelt words you told him. Kind of impersonal, maybe??

Hugs to you