He separated from other Muslims based on asabiyah. That makes him a murtad.
Whoever is killed under the banner of blind following, who calls to tribalism or supports tribalism, then he has died upon ignorance.
Source: Ṣaḥīḥ Muslim 1850, Grade:
Sahih
He is not one of us who calls to tribalism. He is not one of us who fights for the sake of tribalism. He is not one of us who dies following the way of tribalism.
Source: Sunan Abī Dāwūd 5121, Grade:
Hasan
Ibn Taymiyah (RH) said: "Everything that is foreign to the call of Islam and the Qur'an, with regards to lineage, land, nationality, schools of thoughts and methodologies, then that is from the calls of the Days of Ignorance (jahiliyah). Once the Muhajireen and the Ansar argued, such that one of the Muhajireen said: 'O Muhajireen!' (meaning, come to assist me) And one of the Ansar said: 'O Ansar!' Upon hearing this, the Prophet (salla Allahu 'alayhi wa sallam) said: 'Is it with the calls of Jahiliyah that you cry out, while l am still amongst you?!' [Reported by Al-Bukhaaree (8/137)] And he became very angry at that."[Majmoo'-ul-Fatawa (3/456)]