Emerson
May contain jokes =>
The idea is that its rape by omission. That is used like with STD's where you're unaware of the circumstances and it affects you in some way that you normally wouldn't agree to.
Its frankly bullshit that anyone thinks it applies to trans people. Suddenly knowing you had sex with a trans person change the situation in any way for you
I'm fairly certain I've read at least one news story about somebody being charged with rape for tricking somebody into having sex with them by lying e.g. a man pretending to be his twin brother and having sex with his brother's wife.
If so, it's really not a far leap at all from something like that.
Obviously, the rest of what he's saying is hateful shit.