It pulls in higher levels to fill in so you can actually play. Your queue times would be incredibly long if you had to wait to find someone who is your "level". I would rather play 2-3 games and get matched against higher level people then have to wait an hour just to play one game with people of my "level". Also what were the level of your teammates/theirs?
All the queue's mmrs are supposed to be separate. They don't effect each other so the fact that you were against silvers doesn't mean anything(in regards to the matchmaking system at least). If you treat it like ranked, everyone should technically have their own "elo" or mmr and as it is a new system, everyone is technically around the same starting place, so you will raise/drop dependent on your skill.