what is with matchmaking... seriously tho i want to know

so im playing normal blind and almost all of my games have been retardedly one sided.

why ? because among the lvl 20s there is a random diamond player.

please explain to me why i with no good runes, and incomplete masteries keep going against high diamond players

latest example, a bunch of under 30s vs a diamond 4 who was master tier last season

http://www.lolking.net/summoner/na/30723815#matches/2212367726

i thought the matchmaking system used mmr to make a competative game. yet that game the mmr was 1100/2300