Being able to self-fellate is unusual and so it's considered an extreme masterbatory act. I would put it in the same class as tasting or swallowing your own semen. I'm not suggesting that either are wrong or "homosexual".
Straight men will masturbate using their hands or a sex toy, with or without lubrication. This is so common, it's considered a straight act.
Homosexual men may well often give oral sex to their partner, and in some cases swallow semen.
Considering the above, the act of self-fellatio would clearly fall into the homosexual "band" and I would presume that's how many would automatically percieve it. In actual fact, a man will pleasure himself in the best way possible. I expect you'll find that men who can self-fellate do not necessarily consider themselves gay and moreso, many hetrosexual men wish they could.
In summary: It may appear "gay", but it's not. It's just "gettin' yerself off".