I don’t think a 4 year old has the mental capacity to ‘come out’ as gay, straight, trans, bisexual etc. Someone can say ‘looking back I always knew I was trans’ but you’re looking back as an adult. As a small child you don’t really have a proper understanding of things.
Trans is not in the same category as knowing you are gay, straight, bisexual though. Trans is not a sexuality it is an umbrella term for other things and for men that includes dysphoria (which seems to be like anorexia or bulimia in terms of a misperception of yourself), but also having a sexual fetish for imagining yourself as a woman. Hence all the posing for photos in ladies toilets etc.
He does seem to have an eating disorder so maybe when he was 4 he did have a lot of distorted views about himself and his body, but that is a psychiatric issue, not a coming out, alternatively, is he saying that when he was 4 he was experiencing sexual arousal if he put on what he perceived to be women's attire? I wouldn't boast about that. But that is why it is hidden in a catch-all term 'trans', so people don't realise that the genuinely distressed are lumped in with blokes getting off on wearing womens clothes.