Knife makes sense as a backup, but holding it together with a pistol does not seem to make sense.
This is SIG MCX. It’s inspired by AR-15, but it’s a different gun. For example it has no buffer tube (which allows the stock to be foldable/detachable/etc.) and it has a short stroke gas piston instead of a direct impingement system.
In this case the barrel is really short, so the gun would be classified as a short barreled rifle. It’s possible that it’s chambered in .300 Blackout instead of .223 Remington because the former works better with shorter barrels. For .223, this barrel would be comically short and the muzzle flash would be huge.