An unranked account trolled the silver ranked match

I'm silver II main top. My question is Why was it possible that an unranked warwick appeared in my ranked game. He banned my champion during Champ Select and he took my farm in top lane destroying my minion waves making it push to enemy side as so I couldn't farm anymore as the enemy freezed the waves. I don't feel rage but I'm confused as I haven't met any unranked ppl during my ranked game. How an unranked account appeared in a silver ranked match?