This is bullshit, all he showed is that dominion uses dell machines that allow you administer them remotely. That doesn't mean internet.
Also, it is standard practice to disable booting from anything other that their hard drive. Do you think no one will notice a voting machine rebooting?
The ballot scanning machines are networked to a server (over wifi or ethernet) at the site that adds everything up. And the server is where they do adjudication of misread ballots. They don't have to be on the internet.