Taking this node at face value, I am going to go out on a limb, and treat it as a getting to know you node.
A straight guy can definitely be a gay flirt. Back when I was young and furry, in high school, one of my better friends was quite flamingly bisexual. Pride rings, rude T-shirts, everything he could do to tick people off. But have no fear, he wasn't simply posing - since then, he's dated a few men and a few women, and been equally happy (or unhappy, but that's another node) in his various relationships.
As I said, I was young and furry, and had barely started to flirt with girls, and the thought of flirting with a guy had honestly never crossed my mind.
He was convinced that I was flirting with him, sending him signals, everything. The fact that I professed to be straight stood for nothing in his book, nor did the avowal of a mutual friend, my girlfriend (but that, too, is another node). He was convinced that I would make a wonderful gay boy, and I just didn't know it yet.
Eventually, he moved to another state, and I never really made enough of an effort to see him when he was in town, somewhat motivated, I admit, by an effort to avoid being hit on. I was never particularly angry with him - it was just hard to keep telling him that no, I really didn't want to hold hands, and no, I really didn't want a kiss. As Randofu suggests below, I did consider it a compliment, just one that was very very hard to deal with because I didn't like telling him no all the time.
I still consider myself pretty straight arrow, although I have learned the fun that flirting with guys can bring. But I always try to make it clear that it's all in good fun, and that I prefer my intimate companionship to be of more of a feminine nature.
So yes, a straight guy can be a gay flirt. For the majority of my sexually aware life, I seem to have been one, quite unintentionally, and now, now I only flirt with guys I know and trust not to take it seriously. Fewer people get hurt that way.