How do placement games work?!

I would love to know how the initial ranking system works. For example, last night was the first time me and my buddies played for Feb 16’ season. We won the same games, lost the same games- I had a 1.55 KD in the initial 10 SWAT “placement games” whereas a friend had a 0.99 KD and he was ranked higher than I was. Can anyone explain how this system works, slowly driving me insane.

I think it’s also based on previous seasons rank? was he higher ranked than you last season?