5 man premade vs a duo and 3 solo players

is there a bug in matchmaking or maybe the 3 solo players were 3 man but why would i be grouped vs a 5 man if i duo. As expected they had really good rotations and executed dives perfectly. I have to admit i was not playing my best as i was playing gp a champ a am trying learn but anyways i think this should be fixed. p.s i was a normal so i do not mind that much but i hope it does not happen in a ranked game also did not know where to put this in the boards