i might have discovered a boosted/bought account

I joined a ranked match and was surprised by my mid laner, I then went to op.gg to search him up and I found out that he is a plat but has 31% winrate? and also the player that was playing with the account before (boosting it) was an adc main and had 60% winrate with vayne, then you suddenly see a huge change in the account, it stopped being an adc main, started loosing a lot of matches and the overall performance of the account was no where near being plat elo.