Armed Autonomous sentries have been available since the 70's at least.
As for the size of the system, the Navy HAS a 500 foot destroyer to house them. The system itself has been small enough for vehicle mounting since at least the 60's since that is when the Soviets fielded the ZSU-24/4, (We already had the man portable "Red eye" SAM )
The only real innovation is that it was built by a couple guys, but even that is old since the video is from quite a while ago.