In practical (non legal) terms possibly if it was an actual private party and not a licensed dealer.
Alien is definitely a unique way of putting it. I guess it makes sense in that they are “alien to the nation”. But If I were to ever be forced to move to a different country I’d probably go by ex-pat.
Although I’d say we have more of a culture (increasingly so) of acknowledging immigrants as Americans first. Probably due to the whole melting pot thing. My view of it is anyone who immigrate to the US is an American. But if I moved to another country, like Japan, I don’t think they’d consider me Japanese.
Also that reminds me alien ≠ immigrant. Aliens would be people in the country either temporarily or illegally. Someone who got a green card by marrying an American wouldn’t be an alien for example. If you do the whole immigration thing you’re just an American not an alien.