Accurate Intentional Feeding System?

I'm not sure if this is where I'm supposed to post this type of issue since this is my first time making a post on any type of board. But anyways. I recently started ranking again to attempt to get the Diamond rank before the end of the season. A little bit late I know, I just did not want to deal with the "solo queue cancer" people talk about. So, the games I've played for the past few days I have not had a single troll/intentional feeder in my games from Plat V to Plat II until today. I queued up with my friend to duo with him and we get an intentional feeder in our game. I thought they were just having a bad game, then I moved my camera to mid to see that they were going to the Tier 1 tower to sit there, auto minions and let the enemy laner purposely kill them. Then I assumed maybe they were lagging, I then recalled to check their match history and realized that they were feeding. On Purpose. I've linked their NA League account, there is the proof.

There were 2 things I wanted to know with this post. In the recent patch, 5.18, it is said that "The system can detect intentional feeding." Even though they intentionally fed 11 games before the one they played with me in. What does it mean that "The system can detect intentional feeding?" And the other thing is will I be able to get the 16 LP back that I lost from playing with an intentional feeder, even though your system should have already detected it?