How large a percentage of the population of modern Bulgaria can trace their lineage to the turkic Bulgars that migrated there and from which their name derives? Does the lack of a link to the people whose name they carry make them not Bulgarians? Now replace "Bulgaria" with "Vandalia" and "the turkic Bulgars" with "the germanic Vandals", and that's your answer.It is worth considering that the Vandals in Africa were much more insignificant than the Visigoths and Suevi in Spain (there were actually more Alans in the Geyserich army than the Germans). So by that time the conquerors will dissolve among the locals.
The state that governed them ITTL was first called the Kingdom of the Vandals, then the Diocese of Vandalia, and then the Emirate of al-Andalus, which ITTL is an arabization of the word Vandal. The population of Vandalia have been called Vandals by everyone, including many of their neighbours, for some four hundred years at this point. Whatever identity their ancestors might've had, that kind of ethnic label eventually starts to stick.