In all fairnes, Genesis P-Orridge didn’t identify as traditionally transgender but as "pandrogenic" a term which so far applies to only two people/one person and was an attempt to merge with her/his partner to become one identity. Then you have to look up that the preferred pronoun isn’t "they", "she" or "he" but "s/he" or "her/his". During the most high profile part of P-Orridge‘s career s/he was a he.
I don't always agree with Athos, but in this case it’s a bit of unfair to call him out for purposely misgendering P-Orridge. Slip-ups happen and all you can do is to learn and try to remember. Accusing others of purposely misgendering an individual when it likely was a honest mistake isn’t helpful.
edit: corrected because I made a mistake too, these things are tricky to navigate in terms of language