It is not a settled matter of law that the protections and rights provided by the Constitution to "the People" extend to non-citizens, even when those non-citizens are legal immgrants with long-standing ties to their community in the United States.
This is wrong. From the article you linked to,
Courts have held “the people” of the First and Fourth Amendments to include noncitizens, even including illegal aliens inside the country
And note that this part of the article cites earlier US Supreme Court decisions, e.g.
United States v. Verdugo-Urquidez, 494 U.S. 259, 271 (1990) (holding that aliens receive constitutional protections when they enter the country and have “developed substantial connections”)
What the article makes clear is that gun ownership by noncitizens hasn't been directly ruled on by the Supreme Court yet. Some district courts have ruled on legal permanent residents having this right (1)
Others have said that for temporary visa holders, they don't have the same right (2)
Of course, this is not to say that the SC cannot upend existing settled law. By reversing Roe vs Wade, they proved that they can. But that's different from saying the law hasn't been settled yet.
(1)
The District of Massachusetts, in Fletcher v. Haas, ruled a state law unconstitutional because it categorically excluded noncitizens from firearm ownership. The court found “no justification for refusing to extend the Second Amendment to lawful permanent residents” because they have “developed sufficient connection” with the United States.
(2)
In 2012, the Eastern District of Arkansas ruled that a state statute barring temporary visa holders from purchasing weapons was valid. The court distinguished Fletcher on the grounds that it applied only to permanent legal residents, and an open question existed as to Second Amendment protections for temporary residents. It ruled that those protections did not extend to temporary visa holders.