It's kinda both.

It's a meme. Lots of cis women get words like that thrown at them too. Like lots of dudes will use this as a lever to demand pics or video from women, to make us prove we're "real." And yes, that doesn't make sense. Plenty of trans women are 100% passable. And on the flipside, I've even seen guys get pics from flustered cis women who took the bait, only for those guys to seize on some random physical feature and claim they're secretly trans.

So yeah, shitty men on the internet often question the womanhood of women gamers, both cis and trans.

But the underlying sentiments beneath that word are both transphobic and bigoted, and they harken to an ugly transphobic trope that has been used to justify violence against trans women. So it's totally understandable if it's very hurtful to hear that, under any circumstances at all.

And on top of that, I'm sure some men do use that as a slur against people they know are trans women, specifically to hurt and invalidate them as women.

I can't really say for certain what the motivation was for the people who said that to you. These people are losers, though. Sometimes it's hard or even impossible, and I don't blame anyone for walking away from an environment that is genuinely too toxic to enjoy. At the same time, I hope you keep enjoying the games you love, and that you find a way to game without being hurt like this.