I do believe boosting is simply done during capture the relay only as seen below:
http://www.youtube.com/watch?v=wC3YjSgMLCU
As you can see you need to do this in a public game as everything in private doesn't contribute to stats. I myself have never boosted but I've come across this before and you know what I do, exactly what Frankie (in the video) did. Road Rage them
What you caught someone doing is found them in a glitch place.
Although I understand your correction, and have seen people boosting in CTR, this was more of a direct boost, the guy would be behind the wall and had a friend on the other team just keep running up to the wall so he could kill him.
I don't use these secret glitch places but that is one of the worst places.. I know them all n I can't imagine he got v far being behind the wall. Plus if u run out of ammo there's no way out.. Also if he wanted to rack up his kill streak surely it makes more sense just go to a more quiet spot on a map and not have to resort to using a glitch place.. its not like you get more points using a glitch spot..