Comment in question concerned what the poster personally experienced, which clearly wasn't a pleasant/positive one. If you want to demand he prove he met Feinstein in person, well, that's certainly within your power as moderator and owner of this space.
But as far as what he owes to the community, I think he doesn't have to explain anything of his experience interacting with someone. He interacted with Feinstein, his takeaway was she is a "senile moron". I for one won't fault him for that, but you obviously have a different take and that's fine.
As an aside, the fact you flagged my comment as well implies very dark things. It is perhaps better I take my leave because I have no interest in enabling such matters. Though it does sadden me, in a deeply ironic way, that an American entity subscribes to such things. People have died to protect the right to speak ill of those in power.