I was thinking,and I made a theory,when Riku talks to Terra he says that someone went out of the island and became atronger,maybe the person who went out was Xehanorth,he could be from destiny islands and when he discovered the keyblade he went to another world.

Just a theory,sorry if it is stupid.

Indeed. In the Xehanort reports, it stated that he was originally from Destiny Islands, and left the Islands for something greater. So, you're correct on that. But, from what I don't get is, How in the world does Riku know this? He shouldn't even know that, since Xehanort's at least in his 60s or 70s.

Yeah,it's strange.but something happened for Riku to be knowing that

Probably just an old story passed down through the generations.

Probably just an old story passed down through the generations.

 

Yet...who knew Xehanort left is the one question I'll never understand...and Nomura'll probably never tell.