So I'll clarify a bit here, since I only barely mention it in the video. Enemies don't simply attack objects they come into contact with. A wall, such as in the video, will have several pathfinding links going through it. These links will be of a Tunnel type. When an enemy gets to a Tunnel link (or any other construction type: bridge or ladder) instead of moving through it, it sends a ConstructionRequest to the game. The game then plans out what the tunnel will look like, and sends out a bunch of orders to different units to destroy or construct tiles.
Ok, so what's cool about this? Well, since I can easily edit the contents of this Tunnel plan, I can make it so that instead of JUST destroying the tiles, the enemy also replaces them with support tiles to prevent collapse. It's a pretty neat, robust, and flexible system. I'm excited to see how I can expand it to help create a better player experience.