[Retired Intelligence Officer]

How can they be legal when they weren’t naturalized yet? Also what is the difference between Citizen and Natural Born Citizen?

[Tublecane]

“How can they be legal when they weren’t naturalized yet?”

Read the article. They were here on visas.

[AnotherUnixGeek]

How can they be legal when they weren’t naturalized yet?

They entered the country legally as immigrants on a visa. They presumably stayed in the country on a visa or obtained a green card, which gives immigrants "permanent residence" status without conferring citizenship on them. These are perfectly legal ways for immigrants to enter, live and work in the US. Illegal immigrants are the ones who don't do any of this.