No he wasn't a Jin. And that Avatar does not belong to any Bijuu anyway.
That Avatar could be the result of having Six Paths Senjutsu which Hagoromo endowed him with. And Six Paths Senjutsu utilizes Six Paths chakra which is the same as Juubi's chakra (9 Bijuus chakra). So utilizing Senjutsu with Juubi's chakra might have granted him the Avatar, though it's just a theory.
But it was said that he was a loser, who needed an "army" of friends to match his brother Indra.
But then again, Hagoromo also said that Naruto was a loser compared to his parents.
Nevermind, Ashura was just that powerful by himself, I guess. Kishi-plot, it's better to not question anything.