Not making this a thing focused on a persons sexuality, its more how people react to it when someone who they are not sexually attracted to (straight guys from gay guys, straight girls from gay girls, gay girls from men, gay guys from women) feels when someone who they would not sleep with or be attracted to in that way tells you your hot or advances on you, how do you take it?
I have had a couple of women in the past (in my early-mid 20s) say something like that, but I just smiled and thanked them, theres only been once where a girl has tried a little more, to which I told her I'm not of that persuasion, which settled things quite quick, I still offered her a drink though.
I don't take any offense to it, infact I take it as a compliment a girl would, kind of cheered me up back then. I don't see any wrong with it. I have myself told a few guys I know to be straight they look hot, and from that they didn't take offense, least not from what I caught from them, so didn't seem a big deal.