I don't see any dead giveaways off the bat. The only suspicious thing is how clean it is. Don't get me wrong, gotta keep you gear in order. But it looks like its straight out the crate an never been fired. No scratches on the stock, magazine, or scuffs on the barrel.
It's hard to tell in the still of the video as it's kind of blurry.
There were plastic mock ups of various weapons in the military that are used for instructional purposes where a real one isn't required at times.
I was looking at the magazine to see if it looks like something you could pull out or it was molded in with the model. The selector and release levers and such, they all kind of look flat and a bit sunken. But all that's coming in from a blurry photo. It could be real , who knows. You could be spot on.
Anyways to satiate my curiosity if it's real or not, I tried to look but I can't find that particular screenshot from YouTube, on any You Tube video!
Then again, YouTube is biased itself with its algorithms and such much less their purposely selected SJW PC moderators which pretty much segregate content to the point where you pretty much have to be almost case sensitive and to the letter to find a particular video that they desire to censor because they like to put things like that in the 'back room' that makes it almost impossible to find it using conventional Search tools. Go figure.