This doesn't indicate that the FBI listened in on any private conversations, blacklisted anyone, tried to get anyone fired, spread lies about anyone, or otherwise did the bad things that people usually think of when they complain about the FBI. And they feared the Soviets and Chinese would infiltrate because, you know, EPCOT has national pavilions run by those countries and staffed by their citizens. And when they found out that pavilions were not allowed to be political, they then decided the Soviets were not a threat. They don't seem to have thought the Chinese were a threat for very long, either.
Basically, this whole thing is just a complaint about the FBI doing their job.