the hero's bow is in TP.... why?

In TWW you recieve an item called the hero's bow, said to have been used by the hero of time. This makes perfect since as well all know that TWW falls of the adult side of the OoT split, however... TP falls on the child side, so why is there a hero's bow when there was no hero of time? The gorons in the mines refer to the bow saying that it was used to defeat ancient evil and was equipped by a hero of old. but who is this hero if OoT was first, is this implying a game in between TP and OoT? thoughts on who the hero is anyone?

In Majora's Mask ( in the child timeline ) Link receives a bow of similar construction, actually called the Hero's Bow. I think the bow of TP may be another one he later got as adult ( when he grew up a second time ) as it's too big to be the original bow from MM. But the construction is the same style.
My personal theory is that Hero of Time Link may have had furthur adventure after MM, just it hasn't been elaborated on in a game..this could have allowed him to leave his bow to the Gorons, and explained some of the "countless tales" told about the legendary hero..about him.
The Hero's Spirit ( who could well be OoT/MM Link ) says he "chose the life of the hero"...leading me to believe he had more to do with Hyrule in his adult life.

It's never said to be owned by the Hero of Time.

Just a "hero".

It could have been a Goron who used it (unlikely) for goodness sake!

Hero doesn't necessarily refer to a Link. There's plenty of Heroes that are not Links- the Hero of Men may not be a Link, and other racial heroes.

But, you might find this article an interesting read- it ponders the idea that there was a legendary hero prior to the Hero of Time, and that this hero is mentioned in both Ocarina of Time and Twilight Princess.