>Part of what is baffling about the Le Roy case is that it seems to combine two equally poorly understood phenomena: conversion disorder and mass psychogenic illness

Note the word "seems" and "poorly understood". They don't know what this is. They are acting on a theory.

In the language of science, they are acting on a hypothesis. Theory does not mean the same thing in science as in ordinary language - in science it typically refers to a well tested model which is capable of making predictions with a high degree of accuracy. It is far-fetched to call most things in modern psychiatry theories. The models are still underdeveloped, bad at making predictions and fail at treating ailments a lot of the time.