Funny enough I just noticed in my latest game that Predator specifically reads "...killed at least two enemy troopers in Close Combat" [emphasis mine]. It doesn't say "killed via a CC Attack". This came up because someone BS Attacked into a Close Combat between two other troopers and killed a trooper that was "in close combat". Does that count?
Although technically the grammar is ambiguous, I'm 99.9% certain that "in close combat" is meant to be an adverbial phrase modifying "killed," not an adjectival phrase modifying "troopers." i.e. the troopers have to be killed in close combat, not killed while they are in close combat. Like, if I told you someone had been killed in a bar fight, you'd understand me to mean that the bar fight was what killed them.
