Trying to get concrete proof someone is smurfing

Stro02 - Summoner Stats - League of Legends
Stro02 / Gold 2 83LP / 89W 56L Win Ratio 61% / Viktor - 28W 13L Win Ratio 68%, Syndra - 15W 7L Win Ratio 68%, Azir - 9W 5L Win Ratio 64%, Ryze - 8W 3L Win Ratio 73%, Jhin - 6W 5L Win Ratio 55%
I am currently in a Gold and under league and this guy recently joined, but he is clearly above the skill level of everyone else. Is there anyway to prove that he is a smurf????
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