I think i know what is happening. Or i am completely wrong as usual. Sigh.
I just finished a 10x10 700 star game with mew losing, the largest empire near me was the Baskurans or whatever, the nasty bugs. They were just slightly ahead of me in all areas, although i had more colonies. Suddenly the frogs won. Never met them. So, i was looking at the major races that were in the game and the Boskarans were not one of the starting race so they were just a minor who grew up.
Maybe this also happened to you.
Yeah I had this happen in my Zerg game (lol, brown Gizurean empire :D sc2 soundtrack ftw).
The first empire i encountered south of me (ring galaxy) was a Naxxilian independent, 10 minutes later they formed an empire.
As i still only had my homeworld, we were pretty much on even footing apart from my superior military, and they didnt even start the game as a proper empire.
I suspect this may happen all over the galaxy :)