Definition of "delusion" in DSM-5

[Shell B]

And similarities between your two examples, don't necessarily mean that the same conclusion follows (because of other circumstances and how the beliefs where reached).  Would you agree, that not all false beliefs fall under the classification of delusional?

There are 195 countries in the world. If a person believes there are 183 countries in the world, that's just a false belief. But if he still believes that after doing a day of library research, then that's a delusion.

Or he's just stupid.