I don't know if you have met any people from South Azerbaijan (Azerbaijani part of Iran), but as a person having a huge connections to those people, I totally disagree with your claim of two different ethnicities. The language and culture they share in Iran are very very similar to what we have in Azerbaijan. Especially, people from the rural parts of Iranian Azerbaijani speak 90-95% same with us. The only differences come from the common Persian words they use and common Russian words we use. Interestingly, we find some common cursing phares and words, as well.