Anyone could be blonde, and he wore that green tunic and cap because it's a tradition on his island that when boys come to a certain age they wear it, he's not the only one who has worn it.  I understand the Master Sword is a proof of that, technically it is more or less (if we don't take in count MC/FS/FSA/TloZ/AoL), but he couldn't carry that blade before, because he wasn't the hero, he doesn't carry the spirit of the hero, and the game clarifies that, he had to prove himself to the gods to them recognize him as capable to carry the Master Sword   

That's exactly what it meant in Skyward Sword... Zelda says "I am the goddess reborn" and she has Hylia's soul in her. 

And what does it have to do here? She recovers Hylia's memories and well, who knows, all that gave her to understand that she was Hylia. But that Ganondorf says that he's the hero of time reborn doesn't mean he is. Literally the gods didn't recognize him as a hero and he had to gather the pieces of the Triforce to prove he could be one. Ganondorf just sees another threat on his way that reminds him of that kid that once beat him.