I don’t think it’s necessarily a green screen.
The whole thing seems staged. Where is he coming from? Where is his security? It’s like he was placed there & told to walk forward toward someone (a staffer?) who is pretending to be a reporter and they’ve told him what to say, and then they edited in the microphones later to make it look real. Maybe to make it look like he’s capable of answering impromptu questions?
Why is everyone wearing a coat except for him?
Where is his dementia shuffle?
The hand/microphone interplay proves it’s fake.