Matchmaking Skill

Can someone tell me how matchmaking works in arena? I was a Plat 2, my buddy a gold 2, and two randoms. One of our randoms has played one game in his entire career and he went 1 and 16 in our match. While the other team had an onyx, two plats, and unranked. How the hell does that equal out in terms of skill? Is it just random skill matchup? Very frustrating and literally impossible to carry someone that low.

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