Not an isekai, it's just fantasy. People use the term isekai so loosely, because it has gaming and leveling elements. But that is how little the isekai part matters in many isekai (or we don't get to that part), it's just a new start, not much of a difference if it was a fantasy and they were born in it.

He "time travels so it's isekai", time travel doesn't make isekai. Fantasy genre already existed, isekai is fantasy, but not all fantasy is isekai. It is close to isekai, that is all.