Edit: Nevermind. I didn't see the YouTube link, only the screenshot. Simple answer: The shotgun doesn't attack in the video.
I don't see any connected attack nodes there, so my guess is that it's simply because you're looking at the wrong team. In matches against other players, your team can start at either the bottom of the arena, same as in single player, but also at the top. Check the colour of the bots. Alternatively, you may not have assigned this AI to your Shotgun bot for multiplayer, so it's using your Assault AI by default.