Why did my (26f) boyfriend (27m) say I’m only “Average attractive”?

My boyfriend and I just spent a wonderful weekend camping, and as we were just waking up on our last day he (unprompted) said "to be honest, and don't take this the wrong way, but you're not sydney sweeney attractive you're pretty but like, average girl pretty" and I know I'm supposed to focus on the "you're pretty" part, but why would anyone feel it's necessary to tell their partner out of the blue that they're kinda average?? I already knew that but it hurts to hear it from my partner, and since he said "don't take this the wrong way" I feel like I am the unreasonable one for being upset, I don't really have a lot of people to talk to so I figured I'd complain a little here…