Not necessarily (did I spell that right? I hate that damn word!). If he's an "ass man" it might just mean he really finds butts attractive (more so than breasts, for example) or that butts turn him on the most (though anal sex is a possibility.
I like to think of my self as a "girl man" (ok...that didn't come out right...
In other words, I love everything about girls! Love 'em!