It wasn't the extradition that I was confused by, that I get. It was the arrest. I thought extradition only applied to people who had been arrested in one count

It wasn't the extradition that I was confused by, that I get. It was the arrest. I thought extradition only applied to people who had been arrested in one country for another crime and were then being tried in a different country for a different crime. I didn't understand that the Spanish police would arrest somebody on an accused crime commited in another country.