Went 3W 7L in placements but i got Silver 3 when i was placed Silver 5 last season.

Didn't riot say that you start lower than where you were placed last season? I placed at silver 5 in season 7 and ended at silver 5 because i didn't like ranked at the time. When I did my placements this season i got 3 wins and 7 losses so i expected to be in bronze but i got silver 3 instead. Not gonna compplain but I'm really confused. Can anybody explain or clarify how ranked placements worked?