Strange. At first I was concerned about an entire frame slipping in somewhere, as these kinds of things can happen in the editing process. I have a decent process for checking for those faults, though. This looks much more like an encoding or playback error.
This kind of encoding error may have happened on my end, but it seems a little less likely to me. Can you give the details of the file? Format, exact size, checksum ideally? I wouldn’t be surprised if it’s something someone transcoded into a smaller file to throw on a public tracker, but perhaps not!