Silveira, it is great that you found that piece of art.
I have been long insisting in that the Visigoths went Moors all along and on different forums. This can be attested by reading any good History book about Spain, be it from an old or a new author.
It was the Visigoths who called in the Moors to support them on a rebelion, and it was them who first converted to Islam. And it was their descendents (among others who also converted) who were expelled from Spain for being ''Moors'' (i.e. Muslims).
From various sources I suspect that, where the treacherous people who called in the Moors, the party of the family of Witiza, were more pure Visigoths, those who fought on the side of King D. Rodrigo were a mixture of Hispano-Romans (i.e. romanized Celtiberians) and more civilized (romanized) Visigoths. In fact some authors suggest that the conflict between the party of D. Rodrigo and that of the Witiza family may have much to do with this fact.
It is also worth to notice that the Visigoths never got to set full domain in the area of Cantabria, as the population was overtly hostile to them in that mountainous region, just as with the Romans (there was never a full domain by the Romans, but their presence was limited to borders military garrisons much as in the borders with Germania). As such, they had to appoint a local chief as
dux (later 'duque') to avoid trouble. Notice that Asturias, the region where the process of Reconquista 'officially' started, together with modern Cantabria, are the area we are talking about now. That means that the Visigoths would have never retreated to such an area, and would have most probably considered the Moslems as a better option than to have their heads chopped off by those highly hostile peoples.
So much for the Visigoths reconquering Spain. The Whimpigoths! ;D