Boosting in LoL

I just started here this month, and I think I just encountered the first time someone was boosting. I went to go play Twisted treeline classic, and selected Nami for support. Surprisingly, These lv 11 that I was playing with all had ghost and heal (The starting skills) and was, for what I could only see has intentionally feeding one guy on the other team, Brand. The same was going for two guys on the other team, who also played as if they just started the game. My guys were running right into brand, and clearly they knew what they were doing, because they stopped themselves from attacking, and kept running right into towers. The two other guys did so similar, but as Nami, I couldn't really wreck them. Brand, however, actually played like a competent player, and seemed to feign ignorance, but after seeing that the everyone in game was lv11+, I knew something was up.

I thought that with matchmaking like this, this garbage wouldn't happen, and to be honest, that game was terrible experience. I couldn't even just pretend they weren't there because they kept feeding Brand, and Nami just isn't cut out for leading. Seriously though what gives? What does boosting accomplish in this game?