Is this an iCloud sync/backup or do I have a data leak?
The picture displays the playback controls on the device. The name listed that you point out (the "data:video/..." part) is actually a description of the last thing you've played back. 

In case of internet content on a web site for example, this would typically be a URL for a video file.

In this case it is actually a URL starting with "data:". This is a special URL that is constructed so that the actual contents of the video is actually embedded in the URL.

This is becoming a more popular technique on web page to embed content (icons, graphics, small "gifs" or similar) on web pages without having to refer to external resources. I.e. this content appears instantly with the rest of the page as it is actually loaded with the source of the web page itself.

To sum it up: What you're seeing is perfectly normal. It is not a data leak, nor does it have anything to do with an iCloud Sync or backup. It is just an indication that you have recently visited a web page (or similar) that featured a piece of embedded content.