It’s not because young trans people can consent to transitioning. Consenting to sex is not the same thing as consenting to medical procedures. Would you forcibly hold down a 12 year old to give them a vaccine despite them refusing and resisting? If not, then clearly you recognise that under 18s have a degree of bodily autonomy and have to consent to the medical procedures they receive once they are mentally capable of understanding and expressing a choice on those procedures.
It would be pro-trans given the habit of surgical mutilation of intersex infants, which causes a lot of problems down the line for trans intersex people seeking transition surgery that would essentially reverse the mutilation they experienced as infants when they couldn’t consent.
If they meant it in an anti-trans way then they would be factually wrong insofar as transition procedures are, by definition, consensual. The non-consensual procedures (which may be the same procedures) are done to “correct” children’s (usually, though some cis adults opt to have them done) sexes towards the one they were assigned.