So you cannot do ANYTHING other than use your shotgun. If you heal someone, it resets, throw a nade, resets. It is either broken, or just poorly worded.
It's more than likely a bug or an oversight of their progression system. Something I feel could be easily fixed. If you want to try and get it before they fix the issue, I'd suggest going into a squad deathmatch on the empire state map as support, hiding away in the upper floors and take yer time in offing anyone who tries to come up there. Itll take a decent many attempts, but eventually you'll likely complete it.
