I’m approximately cishet, and I approve of this joke, for whatever that’s worth.
I agree that it wouldn’t be okay for cishet people to make this joke about gay people. For one thing, that would be punching down at the systemically oppressed, rather than punching up, and that matters.
That’s really pretty! I am unreasonably tempted to try to make one myself, but it still feels irresponsible to get a bunch more keyboards than I need.