So - you have to download it through a normal browser. The zip file contains a folder which contains the game files. If he had packaged the game files inside of the zip but not inside of a subfolder it would have worked on the Itch.io client
Thanks, I figured that would probably work but I didn't try it. I'd feel better running stuff through the itch.io client with the sandbox enabled though. Just for security purposes. Maybe I'm being overly paranoid but it makes me feel better.