It's a nonsensical tweet. What he's saying is that men who threaten rape to individual women are unlikely to know whether those women are actually male or not.
The perception element is not the issue with this tweet, and men who don't identify as women are also covered if it's in line with existing law. That's understandable but it's going to be vanishingly rare that people genuinely mistake an MTF or any other man for a female person.
The problem some people can see is that being a woman isn't about wearing a skirt or having long hair, it's about being female.
If all MTF trans people are considered "women" for the purpose of a misogyny law then "hate crime" in the extremely flimsy way it's applied in the HCA could be constructed about men who make little effort to "pass".