I assume you're referring to the demo at sketch.metademolab.com? The server is returning an .mp4 file that is displayed by your browser, so you should be able to download it. On Chrome, if I maximize the video and click the three vertical dots, I get the option to download the video.

Thanks. Yes, I figured it out :)

On the online demo, you can also download by clicking 'share' at the end (there's an option in the menu that shows up).