Chocolate literally means "chocolate," but in this song, it's used as a slang term.
"Purito chocolate" is a colloquial expression in some Latin American cultures, particularly in the cumbia genre, to describe something as pure, authentic, or of high quality. It implies that the music or the feeling is genuine and delightful, just like pure chocolate.
Y Qué Pasó? is a breakup song dressed up as a party. Over bright cumbia horns, a woman looks straight at someone who used to be gentle with her and asks the only question left: what happened to your love?
She keeps a running list of what she handed over. The affection, the days, all of it given away and now being handed back. The sting is not just that it ended, it is that she has to rethink the whole thing. She says she will end up believing they never lived those days at all.
The chorus turns that into something a whole room can sing. Tanto cariño, so much affection, and nowhere for it to go. Between the verses the band steps in to greet you, name the singer and remind you they are still handing out purito chocolate, their own nickname for the sound. That contrast is the point. The words are about losing someone, and the music will not let you sit still while you hear it.