I'm sure its either that or your actual player level. I've done placement matches twice this season because i have a second account i use when i play with friends that suck or after i've had a few beers
Anyway, i think how it works is by assigning you an estimated rank based off your player level, then adjusts according to your placement performance.
E.g. if you're a level 300 player it may start you on 2500 before placement then move you up or down, where as if youre a level 25 you may only start on 2000.
Its only a theory but during placements on my main account (level 270 - SR 60 last season) i played terrible and placed at 2800 but on my second account (level 25) i played 10 fantastic games but only place at 2450.