And what if that had been a teenage girl being beaten up by this group of Male bodied thugs?
If a teenage girl got beaten up for saying you need a fanny to be a woman, even without insulting her attackers she'd be crucified - "this cishet oppressor deserves everything she gets" - which if you squint a bit looks a lot like beating a girl up for the crime of being a girl (and knowing it).
In the case of this incident, the victim was essentially assaulted for the crime of "being provocatively cissexual in public".
Always important to remember the appropriate comparator, though. What would happen if four transmen beat up a teenage girl for saying you need a dick to be a man? How would the courts view that, and how would the sentencing compare? I'd lay money they wouldn't just be looking at a slap on the wrists.