Can anyone explain this to me.

[Cynric]

That's also true, but I'm still curious as to how it matches up players. It obliviously doesn't match based on rank (seems anything without two tiers is fair game for being matched)

I think if no one matches its ranking criteria it just throws in whoever is in the queue. Late at night I get tons of unranked players, where as primetime I get more golds.

Though I have no idea how it chooses to balance those players on teams against each other.