Even if apps store stuff internally, and other things can't find it, the owning app can give temp access to another app. Ie, if you click on it in the torrent software, it should be able to find the relevant media player etc and open that media player playing the file.

Not defending this though, it's fucking stupid for them to do it that way, but just pointing out it's not totally useless as long as they allow you to tap/open it from within their app.