Trespassing is usually subject to a LOT of interpretation. If a news reporter showed up on scene, they 100% would not be accused of trespassing. If DG hadn't picked up the light, he probably wouldn't be, either. The question is: Did someone on site actually ask him to leave, or was this accusation leveled at him after the fact.
None of that even matters, because it is an ad hominem against him, also a red herring, and that isn't the right kind of argument to disprove the essential thing he is saying, that the NTSB isn't really doing their job according to their purpose. That light shouldn't have been sitting there for him to pick up.