Like you say we probably don't know all the facts and, even as a young gay guy, having a woman grope me wouldn't bother me in the slightest. However, some gay lads would and I think they have the right to be bothered. So whilst I wouldn't have complained in that situation, I wouldn't blame anyone who did.
Not everyone will agree, but I think there is a difference between young lady groping able-bodied man and able-bodied man groping (any) female. I wonder how many people, male and female, would agree with that? I don't think that the law makes such a distinction; should it?
That's going down a very slippery slope. I think everyone should be protected under the law and not just women. Why should a Woman get away with it if she gropes a guy but yet the guy faces the full wrath of the law (and the social stigma) if he does the same to a woman? I'm in no way anti feminist but women already get away with a lot, particularly when out drinking. Hen's and groups of women in general do tend to think they can grope who they like and, even in straight bars, it's not always wanted.
But if we go down the road you suggest.... what happens if a guy gropes a guy? Is that ok? In effect, the guy isn't groping a woman so it's ok to grope a man if we stick to your view. Ironically however, as a straight guy, (i'm assuming) your view on that scenario is probably very different as you're straight. So why shouldn't the (gay) male crew member feel uncomfortable/offended if he is groped by a (straight) woman?
Just playing devils advocate.
Incidentally, as a crew member myself I have been groped many more times by guys on stag parties. Obviously it's a piss take but i don't look/act gay it's just the usual cabin crew stereotype taking over.