If you look at the very end of the second video, you can see that the camera pans behind the cameraman and shows a bunch of people trespassing beyond the barricades. The position the police were defending was already compromised.
More surprising is that this protest wasn't a "flash mob" - it was planned and known about publicly for weeks - even promoted by the president. Why were they so unprepared?
Certainly possible that the explanation was "sheer incompetence" in both cases.