Help!!

I was scrolling through instagram on my phone and my boyfriend of 6 months was watching. Then I came across a picture of a girl in the ocean with a white shirt on and it was wet so her boobs and nipples were showing. He got a boner from it. I don’t have big boobs i’m an A, and he says he doesn’t care about boobs because theyre pointless and booty is better. It makes me self conscious that he gets turned on by something I obviously don’t have. Do all guys get easy boners by seeing something sexual?