Ah, its a ukelele. It looks so much like my ( former ) Spanish guitar that I thought it must have been a mini guitar hahaha
Ever seen the 1970s movie Deliverance? There's a scary boy playing ukelele in it. This is one of my many, many favorite movies!
Found the scene. Guess it's a banjo after all but it's a pretty cool duet / duel anyway so here goes:
P.S. I'm kind of in the center of Portugal ( North from the center ), which is actually about 3 hours from Lisbon and over 2 hours from Porto. Closest town is Coimbra but I live almost in the middle of nowhere and don't have a car haha