Boosting is when you feed kills to a friend who is on an opposite team.
I've heard in other games where if your host you can see everyone who is in your games ip and they can then boot you by flooding your ip... But I think in your case the message was in retaliation to him being a douche.. Maybe while shooting at somebody he jumped in felt of you... I've had that happen to me when I play hc...which isn't often.. Where a guy team kills me twice.. Then follows me around and jumps in front of my shots to get me booted. :/
So I rewatched the video as per everyone's suggestions from his perspective. . .You know what he did? He purposely dove onto my Bouncing Betties and self-detonated them with his handgun!
COD should be counting these as suicides not betrayals.
What a loser troll that guy is. . .