Well Its not surprising, alot of lego pieces are just mechanisms you can find in a firearm. Look at me sounding all not impressed....
Quake has obviously poisoned you. It's a minigun, even says so in the video. A chaingun is a type of automatic cannon xP Named so for firing from a cannon-sized belt of rounds, which is more like a chain that a machinegun belt. Edit: Actually, I'm a little off, but still, the video is a minigun, not a chaingun.