Question about placement matches

So I just hit thirty and I decided to just play ranked before season 5 started so I can see how far I get. I finished my tenth provisional match with a grand total of 2 wins and 8 losses (MY MATCH HISTORY IS NOW ALL IN DEFEATS :))))))

I honestly expected to be placed in like bronze 4 with this score, but surprisingly I was placed in bronze 1. My friend said it was because the ranked system calculates your Elo based on your performance in the game also, not only of defeats and wins. And for most of my games, I did do pretty decent, going positive most times.

So how do placement matches, and mmr/Elo in general work? Is it based on in game performance also?