The downloaded videos likely have time constraint applied to them that can be updated when the app connects to the Internet. I don't think the downloaded videos can be played outside of the app.
Oh, it’s app only? That would already be a pain. I think they got into a good groove of saving URLs for later downloading. Needing to load each one on a tablet is ruining the automation of them visiting a friend or sitting in a cafe, socializing and downing a few dozen gb via youtube-dl just hitting a list of URLs in the bg.