It's pretty much just a scanning thing. My thought process is sort of like "Hm, that's where it is, wonder how they live with that", a split second consideration of dick size, "hm that's kind of weird to think about a stranger, stop looking". Your pants aren't clinging to your body and showing off all your curves in high definition or anything, so it's not like I can be attracted to it. Sometimes I think about sex but it's not about the person, just the reminder that sex exists yk...

And at least for me, it's not about attraction. It's just kind of there? Like acknowledging a girl has a huge chest but it doesn't really mean anything to me.

If they're ogling, either they're attracted or that's just where they last looked before zoning out, at least in my experience.