Why this name?

While we were living in Spain, many people asked us about our origin. We were answering 'Somos Polacos' which means 'We are Polish' but what surprised us was another question 'Pero Polacos-Catalanes o Polacos de Polonia?' ('But Polish-Catalans or Polish from Poland'). 

Why are Catalans called polacos?

• Some people say, that Catalans have been called “polacos” because they are… frugal – they work a lot and they save their money;
• The other theory says that it’s caused by numerous similarities in the mentality and history of Poland and Catalan;
• Another version says, that one day during the fighting, fascists mistook Poles with Catalans, which is rather unlikely because people who took part in the fights came from other nations like French, Germans, British and Italians in much greater extent than Polish;
• The most famous and the most likely theory says, that “polacos” nickname came with language differences between Spanish and Catalan. Many opinions say that thisname came from the fact that during the military service by the Catalans in other parts of Spain, their local colleagues one day said that “those people from Barcelona and the surrounding area, speak in a such a strange, incomprehensible language like Poles.”

Source - http://foreignlanguagesreview.com/polacos-in-catalonia/