I'd seen something on this crop up on Twitter other day but didn't really follow up.
I'm not really sure I know enough about this but from what I'm reading up it seems more of a kind of "to make a point in a discrimination case", but I might be missing something? (Or Beeb are at least).
It seems to me like if I claimed to be Geordie. As parents have stated there's no black roots in her ancestry, just a bit of native american though she's claiming otherwise which is maybe a bit of a sticky issue (I think over here it'd be fraud if you incorrectly filled out the census on anything but religion questions). Given at the end of the day there shouldn't be any discrimination based on race it shouldn't matter what race she biologically is*, so it's largely claiming to be culturally black in the way I'd claim to be a geek. (But I know Race is a whole other ballcourt in US, so to be "transracial" would likely be upsetting some status quos)
*apart from on a medical standpoint, which can lead to some differences in how you respond to certain drugs and such.