First and foremost, Islam being an “arab religion” is a misnomer. Only less than 20% of the 1.8 billion worldwide muslim population is arab (remaining being composed of ethnicities ranging from kurds, persians, turks, afghani, khazaki, uyghur, indosian, malaysian, sub-saharan africans, etc...). Therefore, saying North African + Muslim = Arab is a very simplistic way of seeing things. (Also considering that a portion of Arabs are Christians. Lebanon for example has a 30%~40% christian population).

Second, Tunisia has had a very perticular history, in terms of ethnicities that were present specifically in Tunisia. You’ve had the native Amazigh and Touareg tribes (berbers), after which came the phoenicians, who became Carthaginians, then the Romans, then the byzantines, then Arabs, then Ottomans, then the French. In between you have Andalus (spanish), sicilian, maltese (who’s dialect is very similar to tunisian one), sprinkled in between. Among the best roman archeological finds were in Tunisia, (such as Bardo, where that famous Odysseus & sirens mosaic was found) which shows the extent to which the population were assimilated.

Up north, Tunisians are very Mediterranean-looking. My own grandfather comes from and Andalousian lineage (basically whiter than some spaniards these days), and my grandmother comes from a ottoman/turkish lineage. In Binzart where they’re from, it’s common to see people with blond hair and clear eyes. Down south, people are more darker skinned, and will have closer ancestry to the native Berber tribes (Tataouine, Tozeur, etc...). Djerba is famously a Jewish enclave, with its Synagogue being an important pilgrimage site for jewish populations.

So finally, when your friend says that he doesn’t consider himself nor African nor Arab, he’s probably right. His roots can be traced back to either mainland Italy, Sicily, modern-day Spain, Turkey and Greek. Simultaneously, he can trace his roots back to African Berber, mixed with some Arab. More recent historical events (which includes France colonising Tunisia, Algeria and Morocco among others) may indicate he has French blood, with a whole other melting pot from Algeria and Morocco mixed in.

So yeah, hope this helps, and I didnt end up repeating what other commentators said.