Filming is not obstruting. Cops like to think it is. This is one of the most common types of successful lawsuits. Obstruction usually requires that you physically prevent them from making an arrest. But they like to threaten that they can do it for recording or refusing to give them information. It's supposed to be a lie intended to intimidate. But if they say it enough times as an empty threat they believe it themselves that that's something they can do.