When you watch a video using Sync, like from redtube, you are actually asking the Sync server to find the video in the link and send you what it finds. Same with downloading a video. This is because the Dev constantly has to update the code that extracts videos from websites.

So he knows all the porn you watch.

(I’m just guessing what’s going on based on my own usage of the app and seeing this url. Either that or it’s pure spying and not needed at all.)