Matched up against a high rank

So just now, I joined a simple teambuilder with my friends to play a game of league. We are all bronze 3 or worse (Myself being bronze 4, don't judge). I noticed the enemy Shaco was doing extremely well and seemed very skilled. Wanting to know what rank he was, I went on LoL King, and typed in his username, only to find that he was plat 2 and mains shaco. I have never been placed in a game with somebody this level. The highest ever, was gold 5. Why was he put in the game with us? Match Making Please.