The supporters (is that the right word) seem to agree. The issue isn't that the people were discriminated based on their sexual orientation or gender identity, but because of their sex. That is to say, if they were males presenting as females, then the discrimination is based on their sex of being male because had they been female presenting as female they would not have faced such discrimination.

It seems like a six of one half dozen of another distinction, but I think it may become a factor when you start considering other sexual orientations. Primarily asexual individuals, but there are a number of other characteristics of humans that are currently classified as sexual attractions and not orientations but which some scientists think should be reclassified based on the biological/neurological basis as we better understand the difference between a preference and an orientation.