The idea is, When you call someone "Paranoid", It usually means that its all in their head, or that whatever they're thinking isn't really happening, basically over-reacting, Its more a third party perspective.
This picture is basically saying "Just because they think you're paranoid, Doesn't mean you aren't being watched".
So its like, Just because you think someone is paranoid of being watched by the government, doesn't mean they aren't being watched.