Conspiracy theory from Merriam-Webster. A theory that explains an event or situation as the result of a secret plan by usually powerful people or groups.
A theory relies on a string of events, some of unknown probability. A conspiracy theory treats new information in a unique way.
When an explanation is given for an uncertain event and rather than the broad probability being used to reassess the theory, the sliver of any open issue is focused on, you are dealing with a conspiracy theory.