Is it wrong to acknowledge attractive people around your significant other? What are you supposed to do? Bottle it up and tell only your friends that are separate from your boyfriend? Guys do the same but I have been there when one let things like that slip in front of their girlfriend and it wasn't pretty. The girl threw a tantrum.
Is keeping secrets the answer? Are we supposed to act like our boyfriends or girlfriends are the only attractive people on the planet. That is deceptive. Do I love my boyfriend? Yes. Is he attractive? Yes. Is he the only attractive male? Hell no.
I encourage honesty. If he thinks some girl is hot, I want to know. I want to scrutinize it and analyze what he likes/dislikes about her. I want a greater understanding of what his type is. And I want the freedom to do the same.
I would refrain if it bothered him but it doesn't.
This old fashioned protocol of never letting your s.o. know you find anyone else desirable but them is secretive and just a plain lie.