it's a dogwhistle. they're implying that trans people are mentally ill and that the postal worker is a victim of inaction with or indulgence in the trans population.
It's the same reason why all the chuds started banging out about how violent trans people/leftists are when that trans man (if i remember correctly i did) shot up a school a year or so ago.
despite the fact that the overwhelming amount of school shooters are cis right wing incels