the only reason police stopped the plaintiff was because he was recording video in a public place.
Sure. I accept and wholeheartedly agree, that the guy's recording is legal and should've been unmolested.
I just don't see, how the First Amendment protects him in the slightest. Doing, what is not expressly prohibited by law is legal in a free country — you do not need it to be expressly allowed by an Amendment or anything else.
The only possible charge I could see is disobeying a police order — had they ordered him to stop and he continued, they could've charged him with such disobeying, even if the order itself were later found invalid.