Looks like a damage mod and possibly some form of recoil control. Using the AWS with a heavy barrel he manages multiple times (timestamps in video description) to drop 3+ enemies in what looks to be too short an amount of time while maintaining a very impressive 24% accuracy on 180/180 kills. Does not appear to be burst firing the weapon during the video, always spraying full auto. An odd moment at 26:50 could be a slip up on a wallhack as well.
http://battlelog.battlefield.com/bf4/battlereport/show/1/1028693928288536512/596108493
180 kills - 920 hits. (this is not a dmg hack)
for the video i'll let the moderator decide. (recoil hack is hard to proove in specator mode) and for wallhack (this is metro ... )
I've played a couple thousand hours of metro and getting such a high accuracy and kill count with just an LMG (let alone a high rof lmg like the AWS) is something I don't recall happening before it's that rare (I'm sure it may have, but the vast majority of kill counts closing in on 200 are done with some use of a shotgun). Still looks like a wallhack on that timestamp, metro has nothing to do with it. Of course it could be another fantastic spectator glitch. Not sure how you get hit statistics, but 24% accuracy on a 180 kill game all with the AWS with a heavy barrel is remarkable.
Found another report of him on Dragon Valley Conquest Large. 111/24 22% accuracy. Just seems really off to me.
That accuracy is very achievable especially on a map like lockers.