Soldier would absolutely think he's Mandalorian. He goes around wearing a helmet that he made himself. It's not quite the right design, and everyone can tell that's durasteel not beskar. His clan signet is spray-painted on. He wears barely any armour (he's confused Mandalorian culture so far that he says 'a real Mandalorian wouldn't even need armour' because they'd simply just not get shot. A real Mandalorian would have killed the other guy first. Somehow, this manages to please both the pacifists and the traditionalists in Mandalorian society.) He knows 5 words in Mando'a and he finds a way to insert them into any conversation.

Literally any Mandalorian that sees him is like '?????' but most just shrug and give him an A- for effort, or just roll their eyes and move on with their day. Everyone knows that he's not Mandalorian. His teammates are happy to pretend.

Zhanna is ecstatic when she finds him, though, because she will have a great warrior of a husband, and a challenge in single combat. That is one thing that Soldier has down. He is definitely on par with the best Mandalorian verde, at least when it comes to violence.