There is no "official" language in the USA. Yes, that's true -- you can check it out online or anywhere else you please. However, the language of business in USA is English. People who were born in USA speak English and many (If not most) people who immigrate here try to learn the language even if only to get a better job. But there is no requirement that they do so.
Furthermore, can you imagine how difficult it is to work 8 or 9 hours a day, 6 or 7 days a week, try to raise a family AND ALSO learn a foreign language when there are few if any places that teach it at low cost.
And beyond even that, how do you know that the person you're referring to wasn't a TOURIST? If you traveled to Turkey (for instance), how well would you be able to converse in Turkish?
All of that having been said, I believe it is still in the best interests of immigrants to learn English even if for no reason other than they will be more likely to get a better job.,,,and most really do try.