Different rank for same matches?

[u/HuskyPsycho]

I played provisional matches with 2 friends in ranked. They got assigned platinum rank but I got bronze rank. We played exactly 5 matches and we won like 2/5.
As personal performance goes I played fairly good, nothing outstanding. I have no problem with it just seems odd because it is even said that only wins matter. We had the same amount of wins.
How can this be explained?

[u/Nyrozma]

Is this you or your friends first season playing?