me and my high gol-low plat team have lost 1v5 vs a grandmaster vayne

So. This morning i queued up in a ranked game, and i'm gold 1 in a 6 games losing streak. so my elo should have dropped below gold 1, but somehow i have been matched against a grandmaster vayne toplane. I just want to know why i can be matched against a grandmaster player in such a low elo when i can't party with my d5 friend because of the tier difference. I'm not complaining, i just am really curious about how things work because i can't understand
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