I feel like there is some discrepancy regarding the Xcard as a conversation starter. I thought it explicitly was NOT a conversation starter, but a trigger stopper, no questions asked.
Well, folks use variations.
The most recent and constructive conversations I've seen about it are that the person who invokes the X Card does not
have to explain. But they may, to the extent they want, if they are okay with doing so and feel it would help.
And, yes, it helps the GM if there's
some information. If you can tap the X Card and say, "Spiders!" or "Please don't shout at me!" the GM knows what to avoid. In neither case is the player required to go into depth why - maybe shouting hurts their ears, maybe it triggers their PTSD, doesn't matter, just lower your voice already.
If you tap the X Card, and can say nothing more, well, that's more difficult to manage, but most of the time it is going to be something proximate to the invocation. Like, they're probably not tapping the card over something that happened 15 minutes ago. It is unlikely to be a huge mystery.