Without a doubt the officer handled this badly, but I did find the following explanation of why he might have been right about their "right" to stand on that concrete median if he believed their presence would impede traffic or cause a risk for others.
Time, Place, and Manner
These regulations of expression are content-neutral. A question to ask: Did the expression occur at a time or place, or did the speaker use a method of communicating, that interferes with a legitimate government interest? For example, distribution of information should not impede the flow of traffic or create excessive noise levels at certain times and in certain places.
Also from a constitutional law attorney that I know very well:
Q: in regards to the first amendment, can police remove a film crew from a median?
A: It's always a fact-based analysis, but yes, the government can impose reasonable time, place & manner restrictions on private speech, so long as the restrictions are viewpoint-neutral. If the restrictions are based on the content of the speech, they must satisfy a compelling government interest.
