Generally speaking, these sorts of bans don't happen because of a "win streak." It takes more than a run of good luck to convince the system that it is some manner of cheating happening. If they suspect it was because another player was using your account to boost the elo, then it is based on things like IP login, summoner spells, champions played, kda, amount of inputs per second, and many other factors. Sometimes, it's as easy as going to a person's Match History, scrolling back a few months and seeing them with a huge win streak on a champion they haven't ever played otherwise, with the summoner spells in a swapped position, using a different trinket. Other times, it's not that easy.