It's not the posters video, the poster is only linking to it.
In the US you cannot be detained unless you are the suspect in a crime. No crime and you can't be a suspect. The police can _ask_ for ID (which they usually do, as a "request") but you are not obligated to produce ID upon something that is just a request. The police attempt to hide this legal right by not explaining this and making it _sound_ like you have to show ID. When/If that request fails some (bad) law enforcement agencies will then start making up illegal reason's to obtain your ID, which is appears that they are doing in this case.
But we are getting off topic.
I saw this video yesterday. It's not really about drone flying. It's more about property owners and an animal rights organization not getting along and the property owner wanting the group stopped for "questioning".
Sure, anyone can feel free to give up their constitutional rights in order to avoid an illegal detention. However, this only serves to erode ones legal rights and leads to further abuses. If someone is allowed to get away with something they will probably continue to do the same thing. Some people get pulled over based on the color of their skin. Should these people stop behaving like "jerks" and just allow it to continue in order to get on their way more quickly?
What those people actually "deserved" (that is a light term, as it's actually guaranteed in the US Consitution) is free travel within the US.
With that said, I think this _might_ have been a tough call for the police. Even the police admitted that they did not know if what was being done was illegal. They needed to investigate and make that determination. You could make the argument that they are required to know the laws before they detain someone but it's not always a perfect world. I could see them being detained for 20 minutes or so... but it was something like 40 minutes? The question is if the police were doing this to harras the animal activists on behalf of the property owner or not.