I'm not 100% sure, but there are several reasons. Either your friends totally sucked, and they had 0 kills and tons of deaths, resulting in people "boosting" off them. Same with if they were afk. Your friends also had to be afk or be really bad for several
matches for the system to notice you. But if it is a xp problem for you, you must have been boosting off your friends. Sorry, heh..