I wasn't the person you asked but I don't see anyone answering on the thread, so I will try to. I think it depends on where in the USA you are. I expect most educated people, particularly in larger cities where there are a lot of Iranians, or people who have educated themselves on the subject, will know that most Iranians are not Arabs and do not speak Arabic.
Some people don't know this, unfortunately, but they are decreasing in numbers. For example, in 1979 and through the early 1980's there was a popular "villain" in Professional Wrestling (very popular here) who called himself "The Iron Sheik" and dressed as an Arab but pretended to be Iranian and a follower of the mullahs. He did it because even though people hated the character he played (because of the hostage crisis) he knew they would pay to see him get beat by Americans.
In fact he was a real wrestler who won an Olympic medal for Iran before the revolution, and had to flee after the revolution.
Few people understood then that Iranians (Persians) are not "sheiks", dress as Arabs or lead camels around. But most people understand now.