They are thugs, of course they will. What Catalan club names itself Espanyol? lol
Catalans are a minority within Catalonia contrary to popular belief among foreigners. Most locals originate from other parts of Spain or are a mixture of Spaniards (read people from other parts of Spain) and local Catalans. So nothing strange about that.
It's very common to have a Spanish (read surname originating from other areas of Spain other than Catalonia) surname and a local Catalan surname. In Spain the surnames of both of your parents are traditionally used. For instance Hernández y/i Creus.
Players such as Xavi, Valdés, Montoya, Roberto etc. are actually originally (or their fathers at least) from other parts of Spain. Evident by their surnames.
Catalonia welcomed a very large number of migrants from other pats of Spain (mainly Andalucía) at the turn of the 20th century but also long before that period. Many of their descendants nowadays regard themselves as Catalan though.
Add to that migration outside of Spain entirely which has also been numerous in recent years.
Spain is a really mixed country in this regard and is what makes the country so rich. All Iberians though although some are really hellbent at creating overblown differences when the reality is that there are not that many at the end of the day.