While Havana Syndrome is real, to my knowledge it's not that refined. It should have impacted everyone in the room, Trump and the moderators included.
The known reports of the syndrome occupied entire floors of buildings. The idea that someone could use it and just target one guy is a little out there.
The work done on it has been fascinating. You'd think if it were simple hysteria there would be outbreaks among the civilian population, but it's always government employees.