Who learned the song first?

So we know that Guru-Guru learns the song at some point and realizes its curse, but only after a little boy plays it in the windmill, which means Link must’ve learned it or made it, but at the time of the game he just then learns the song as an adult. Yes he goes back in time and can play it for Guru-Guru, but he only learned it from Guru-Guru. Which means someone else introduced the song to him.

The best theory I have on this is that if the events had gone similarly, Link still would’ve been the hero of time and gone off to look for Navi, leading to the events of Majora’s Mask, where he re-learns some songs including the song of storms. While the whole game supposedly takes place in his mind, there are some clues I noticed otherwise that would beg to differ, like the mirror shield having the face instead of the gerudo symbol. Since Link is 13 at the time he perhaps went back to Kakariko Village at one point and eventually paid a visit to Guru-Guru, playing the song of storms for him as a means of protection (it worked at the gibdo house in Termina) for the town, only for the curse to be realized once again. Just a thought