arab is not used as an ethnicity but refers to someone who speaks arabic as a mother tongue. In the same way, that North africans refer to themselves as Arabs although genetically they are less than 50% Arab.
A whopping ~2% of Iranians have Arabic as their native language. That means, if you're going based on language, you're mislabeling 98% of the population.
Not sure where you got this from, here in Morocco, calling a Berber an Arab is a pretty sure way to piss him/her off.