@No:
Uhm before anyone spews more "Sabo saved by Dragon cuz he said "him"" theories , didn't Japanese have an ambigious form of referencing someone , aka as neither "he" or "she" but a combination of both ?
No, they have a form that omits the pronoun, they can simply write without using neither "he" or "she". And it was discussed already, go look for Aohige's posts if you wish to know more.
But anyway there wouldn't have any purpose to put that scene there if not to give the hint that Dragon rescued Sabo, why else Oda would do a flashback inside of another flashback just to show us that Dragon stopped by Zoro's island, it wouldn't add anything relevant to the story. The moment the flashback (inside the flashback) was showed is also conveniently right after Ace and Luffy make their decisions on what to do from then on since Sabo "died". And the crew is surprised by seeing someone injured when Dragon comes back, and Dragon himself is shown to be alright (there is nobody trying to heal him), so he brought someone along, who only can be Sabo given the circumstances.
@Ivotas:
Lol, that was a cameo appearance of Zoro. The reason why people think Sabo is alive is a different one:
Yes, we have already brought his attention to that.