If the video contains all contact and communication between the cop and the cyclist, then the cop is a thug and a liar.
However, after seeing articles on this event yesterday, I started doing some research on Critical Mass, and learned a few things. There is no organization, there is no set route, and they can occasionally do what they call a Cyclone in order for the slower cyclists to catch up to the group.
The cop and the cyclist could easily have encountered each other, where that lawful order was issued, minutes or hours prior to the video being shot, if the cyclist was on a second (or more) trip around the block.
Good point, thank you!