This is tautological. They’re effectively defining conspiracy theories to be things which are not widely believed, and then proclaiming that the things which are not widely believed are not widely believed…
Their definition of conspiracy theory is found in Appendix A, where they just present an ad-hoc list of things they personally believe are false beliefs. Some of the things they present are very widely believed, and at least a few of them have actually been proven true (more or less).
It's always like this with such papers. 100% of them are pseudo-science.
Okay?