In this given case, I don’t see a problem with that. The site was anti-gun protest. It is a common and sensible policy to divide groups of protesters with opposing views. They could have stayed just across the road and hold their signs all the same.
I understand that US doesn’t have a separate constitutional right to demonstrate like most of the world does and that it is derived in the US from the right of the free speech, but you can’t enjoy your right to demonstrate if your demonstration is being infiltrated by the opposing group. Setting separated areas for various demonstrations is nothing that would infringe anyones free speech rights.
Its the same with these idiots. They are free to express their views, but they are not allowed to run in between the funeral procession.