It probably happened just off Las Ramblas. There are two main groups who thieve, the gypsies and the Moroccans. They all work usually in a groups of three.
The Moroccans like to be quite blatant when taking your stuff by doing the Ronaldhino and pretending to tackle the poor tourist. The gypsies hang back and look to pick pocket people discreetly. Moroccans don't really keep dogs as they are Muslim and gypsies are shit scared of them.
In a decade I've only had my moped nicked and I found it again. My best friend from London got robbed twice whilst she was with me.
They don't want your cards, because they incriminate, they just want your cash. Passports are worth money, especially British ones.
If you get caught beating up one of then the police will thank you for it!