For the purposes of statistics it should not matter in the slightest.
It has to be recorded as committed by a transwoman.
I think it's the same political strategy police and governments across the EU have used to avoid stating when someone of particular religion, nationality etc has committed a certain type of crime. The feeling is that to share that information is in itself a discriminatory act, and they fear being shamed/sued/triggering reaction and publicity because it gives the impression that this particular group is a risk.
Again, this ignores and covers up the underlying issue that while NA(whoever)ALT, there are justifiable questions, concerns and topics that people are being prevented from acknowledging, talking about or having a non-compliant reality to. The Emperor has lovely clothes, ooh look a squirrel'.