Seems like the serie have MC saying he crossed over just to add the reincarnation/isekai tag so it hits more search parameters, a patethic move I've seen many authors do in both manga, manhua and manhwa, but is always patethic.
In this case it seems to be that as he is reincarnated his training started early.
But that is, aside some mental maturity he got no help from being reincarnator, even the way he behaves is ttally like someone from the story world, is just flavour text and nothing else.