Did you feel like it was said in a way where you would be expected to say "thank you" and/ or did it feel like he was expressing his personal preferences/feelings, or did it seem more like an observation? Like was it about him or about you? For me that's what makes the difference.

My therapist has stated matter-of-factly that I'm "very attractive" in the context pointing out that "you have a lot of things going for you" and he said other things first, like academic achievements. It didn't feel inappropriate because he wasn't saying it as a personal compliment that I was supposed to respond to. If he'd said "[academic achievements] and I think you're very attractive" that would have made uncomfortable because the focus of that would have been on telling me that he personally finds me attractive.
Of course, if he went out of his way to call me attractive on a regular basis that would feel inappropriate.