I would say that any claim is bold if it is surprising or apparently important, and is not covered by multiple mainstream sources.
Examples are claims of majority (A majority of people are suffering from sickness A, B, or C), Or claims of superiority (My car is the fastest in the world).
Examples are claims of majority (A majority of people are suffering from sickness A, B, or C), Or claims of superiority (My car is the fastest in the world).