I don't think that's what they were referring to. From watching the video, I assume it was when he grabbed onto the fellow they were detaining and refused to let go.
If you witness police misconduct, you do not have the right to impede the police. Regardless, there was no way for him to form an accurate belief about whether misconduct was occurring. The agents have no duty to provide a warrant to a bystander, even if he is a government official.
