Thank you for that.
Your description of what happens in the video is pretty accurate, i'd say. I would query your claim that they 'show some kind of identity paper', I don't think that is clear at all (indeed, the second person doesn't appear to show the police anything at all), and they were behind the police line for a matter of seconds, rather than minutes (but that's a minor nit-pick).
I'm not sure that I'd be confident in claiming this as proof that these were agents provocateur, but it's certainly not impossible.
Again, thank you for finding the video.