On tablets or mobile devices, like the iPad or iPhones, the browser will try to be helpful by playing the video online, rather than actually downloading it - even when you hit the Download button. It's built into the software on the device, and we can't do anything differently on our end to change the way this works.
The best way to mitigate this would be to install an application on your device that is made for file storage and downloads.
You can find one that works for you by searching "download video ipad" on the web. However, the one we've tested which seems to work seamlessly is Documents by Readdle, available here: https://itunes.apple.com/us/app/documents-by-readdle/id364901807
Once you've installed that app you can follow these instructions to download a video: https://readdle.com/documents/how-to-save-files
NOTE: If you have the latest version of your device you should be able to download it with no issues by clicking the download button.