I remember specifically one time while playing ranked with a friend that there was this guy on the enemy team who had a diamond border from last season even though we were in Silver.
A few minutes into the match I got a double kill from him and his support and he lashed out saying he hated this elo hell and I told him he belonged here because he obviously boosted. (It was meant to put him on a bigger tilt. He was adc btw)
About 20 minutes in and five deaths later the guy logs out for like a minute or so and then comes back suddenly last hitting all the creeps and dodging literally every skill shot that was thrown his way along with the most perfect attack walk I've ever seen outside of LCS. Because he was adc and naturally had a lot of wave clear and push pressure we ended up losing because we literally could not hit him with anything unless it was targeted.
Of course he wasn't saying shit during this time even though he was complaining about it the whole game up until that point. Also since he lashed out to his teammates prior they had no problem reporting him for scripting as well.
Idk if the guy is still playing but I'm pretty sure everyone in the game reported him for scripting because of how obvious it was.
If that wasn't it then it was a legitimate elo boosted account and should be banned anyway.