What I just said sounded unkind. I'll try to explain it better:
One of the worst aspects for many women, including myself, who have been raped or sexually assaulted, is the violation of the image you have of yourself. One minute you're a competent professional; happy after a night with your friends; celebrating your exam results; safe in your home; getting your life together after difficulties. The next you're being held down and fucked. It isn't about sexual desire. It's about power and assertion and domination. It's about putting you back in your box. What you are is a hole to be fucked, and nothing more.
So this trans guy will be traumatised because the rapist violated not just his body, but his image of himself. That is the same for every person, male or female, who is raped. His suffering must be terrible, but it is not somehow worse because he is a trans man.
His delusion was that being a 'man' made him safe from this guy's attentions. It didn't, because rapists don't care about our personal gender identity. I worry for the mental health of all young girls who think they can somehow opt out of all that goes with being female :(