IPSO standards clause 2 and 12 say:
Would the story be newsworthy if it did not concern an individual of transgender status?
Is the individual’s status relevant?
Unless he was transphobic towards them, the second means no. If he wasn't transphobic, their trans status would not be newsworthy, meaning that isn't satisfied. It being unusual does not make it necessary to state they are transgender.
Also covered by clauses 1 and 12 are:
Has the individual made their transgender status known?
if not, is the revelation of their status necessary to the story?
Having transitioned alone does not qualify for this. They have to be widely publicly known as a trans person, and that's hard to define, and is done case by case.