Because this is a huge game of 'The L24 Mole'. There's alot of tell's/clues being given by Lee and now oldman. He wants to keep talking so he can give clues.
An obvious tell is, Rick calls for everyone to just ignore him. That would be ok for anyone but Rick, if Rick really believed he was that serious of an issue to be ignored, he would just ban him outright. So the fix is in.
Second is all his topics are extreemly obscure. Walking fifty miles in a marathon 45 years ago. Running down the Grand Canyon in July 40 years ago with no details. Having different childhoods including guiding when he was 12 or something. Military sniper rifles in '68. All obscure, only an expert can refute. But he is a constuct as someone else coined, a daffy duck so to speak. All you are arguing with is the imagination of the constructer who purposely leaves something just not right in his topics.
Who it is I don't know, but it is good entertainment as it was designed to be.
