A question about Dyna Queue

Early this morning I played a couple games of ranked, and noticed that the premade dyna queue teams were somewhat even except for one game. http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2158010377/207379439?tab=overview In this game we had a 3-man premade vs 3-man premade, but the enemy team also had a 2-man premade as well. Myself and another were solo queue.

I'll use a 2man premade as an example; If a 2-man premade is selected for a game, they will likely be matched against another 2-man group. Shouldn't both teams receive a second premade set equally if there are two available? I guess I'm wondering if it's a bug, or if it just randomly worked out that our solo mmr was equal to their duo or something.