Why is Iran not an Arab country?

Answer 1

As concerns Arabs:

Arabs are people of the Middle East that are united by a common language: Arabic, and a common history: the Islamic Caliphates. Arabs are not necessarily of the same ethnic stock and in many cases are of mixed heritage due to intermarriage between the Arabs coming up from the Arabian Peninsula and indigenous Semites and Berbers. Not all Arabs are Muslim, but all Arabs have (in their history) spent time under an Islamic government.

As concerns Iranians:

The overwhelming majority of Iranians do not speak Arabic (less than 5% do) and actually speak Farsi or Persian (same language). They have a much longer civilized history than the Arabs, stretching back to the Ancient Persian Empires from 6000 years ago. The Persians are the dominant ethnic group in Iran and are Caucasians as opposed to Semites. There are also large minorities of Azeris (who are a Turkic People) and Kurds (who are a Semitic-Caucasian hybrid). While most Iranians are Muslim, this is really the only trait they share with Arabs.