Bronze 5 after 9/10 wins in Flex matchmaking?

Like what? I'm a diamond smurf and just leveled up this to level 30 and started the flex placements, after winning 9 out of 10 games extremely hard, I still kept getting matched against and with Bronze 5-3 players and got placed in Bronze 5? So confused, my friend who did the same also got into bronze 5, wtf rito? Proof of Bronze 5: Proof of 9/10 wins:
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