How do you know if they are faking it or are genuinely interested? You can't. No one can. But I imagine most women wouldn't pretend to like something like games to get attention. The majority of women who profess an interest in things like Sci-Fi, video games or old movies, genuinely have an interest in those things.
Sure, some women fake an interest in things to get attention from men. But how many men have attended dancing lessons for that exact same reason? I know at least 10 guys who signed up for my University's dancing club for the SOLE REASON of meeting girls. It cuts both ways.
If I have no evidence to suggest that someone is faking an interest in something, I assume that they are genuinely interested. I could be wrong, but if I have no reason to suspect fakery, why would I?
You can't tell someone's interests based on appearances and gender. One of my fellow co-workers in my lab had a crew cut, he was fit, cursed up a storm regularly, and had tattoos. And yet he liked to JRPGs. Another woman I knew from work - small, short, squeaky voiced, and had a hobby as a stone carver. Just because a women is attractive, doesn't mean they can't have an interest in things like games or sci-fi. They are less likely to demonstrate an interest because society tells them they shouldn't, but that doesn't mean they don't have the interest inside them.
There's more to life than being suspicious of people's motives, especially over such trivial things as hobby interests. There's a possibility that a woman isn't really interested in what she says she is. There's a possibility of ANYONE faking an interest in something. I can tell you, having studied along side medical students during my cell biology courses, how many doctors-in-training have absolutely no real interest in helping sick people or medicine, but have merely become doctors because A) Their parents wanted them to be doctors, B) Because doctors get respect or C) Because they want a lot of money. And that's far worse than a woman faking an interest in D&D.
People lie. But no one lies all the time. There is really little to gain from pretending to be interested in gaming or "nerd" culture. Even if women really were desperate to meet men, there are OTHER activities they could fake an interest in which would grant them much more success (like cars, football or guns).
And just to reiterate: Men do the exact same thing. I can't tell you how many boys in my Highschool joined art simply because it allowed them to work with the pretty girls in my grade. They admitted to me that was their aim themselves.
And don't assume they are patronizing you. Why would they fake an interest in something to patronize you? That makes no sense at all. Literally no sense. If they wanted to patronize you there's a million better ways to do it.
Don't go through life being suspicious of people for no real reason. I myself am I very suspicious guy - for example, I never give anyone my real birthday and I never fully trust ANYONE. But I don't spend time trying to dissect the motivations of people around me, especially when the activity or interest in question is so trivial to my everyday life. If I see a woman expressing a deep interest in video games, I believe that she is interested. Of course, she might not be. But why would it matter? I have no reason to suspect fakery of interest.
I am much more concerned with uncovering the motives of my bosses and anyone who wants any of my money. On job and financial matters, I trust NO ONE 100%, whether they be male or female.