What Does It Mean If Your Partner Says “thank You” After Intercourse...?

I think I’m a little confused by the term partner. To me it connotes a long term relationship. In that case, a thank you would seem odd.
If you’re using the term for a casual relationship it wouldn’t bother me. I go to male LMT’s and some include a very interactive happy ending. It’s common for them to thank me for a great session. I scratch their itch and they scratch mine.