Probably because he sort of "reincarnated" back to his young self, despite not dying.
but i see the reincarnation tag on normal fantasy manga too, like
Kouryakuhon o Kushi Suru Saikyou
You sure? I have that on my list, and it doesn’t have that tag on it. Maybe it got removed... Or the story is just similar to reincarnation stories, so it’s placed as a tag there
on the right side, first row
Those are suggested tags that readers use, it’s not the actual tag for the manga.
why is there a reincarnation tag lol