I used to work in Spain and it broke my heart every autumn when we went to the coast, to see the 'pariah dogs' - either abandoned throughout the summer or whelped while Mom was on holiday and then the whole litter abandoned.
They would form gangs and scrounge and scavenge food from the hotels, but as the tourist season came to an end, many of these would close and the whole pack would starve, or be run over - and vanish. Anyway, by Christmas there would be no gangs of these dogs roaming the streets.
You don't say where he was found but it is very possible that he didn't originate in Spain but in France or Germany. None of which is really important. What is is that he has found a wonderful forever home with you.
Standing sideways on, yes - it would definitely seem that there is Basenji in him somewhere. He has the right stance and outline and although tiny, it isn't impossible. And from your description he has some of the right characteristics too.
I am starting to disbelieve many of the DNA test results - they are too 'way out and extreme, but you could have him checked just to see what weird and wonderful combinations they come up with.
But just enjoy him - don't worry too much !