I think the bigger question is what's the thing with all these types of threads and everyone being so concerned about what everything means to someone else? Not picking on this thread, just these types of threads in general since there's 238958 of them. Sexuality isn't something that is black and white (unless we are talking interracial porn of course). There isn't one answer, everyone is different. It could be denial, exploration, taboo, empathy, or just plain not giving a crap about putting sexual preference in a box. I don't think there's one meta answer that it seems are often being sought in these type of threads, or vice versa a conspiracy that every dude who looks at cocks is secretly in the closet. Like Daisy said, when women look at another woman's body no one is psychoanalyzing the motives. But rejoice women, at least there is finally a double standard that applies to men instead of women.
Now back to your regularly scheduled masturbation.
Absolutely!
Why do we care why a man is looking at peni? Well, for one, he has a penis himself... That makes you quite curious to know about others'. But many other reasons as you stated apart from curiosity: insecurities, comparison thrills, jealously, pure gay attraction, etc...