perhaps you can send a joke to him such as "thanks for thinking of me" or "thanks for meeting me at the elevator". even he did not say anything, making it a casual flirt. better than feeling guilty or making him feel guilty.
people sometimes say thanks for you when you forgot to say thanks. a humorous way to remind that he does not have to be that way.
just a thought.
Peronally I once said "torture again!! you know how to torture people, do you" and laughed it away. and both relaxed.
