Re-read the abstract, but replace "glymphatic function" with "restaurant spending". I'm pretty sure that a study would show that PWME spend less in restaurants than healthy controls (we feel too lousy to enjoy the experience, plus risk of PEM). It's easy enough to claim that less spending in restaurants "may lead to symptoms such as cognitive dysfunction and sleep disturbance experienced by ME/CFS." Spending probably correlates with severity, and probably also has a gender bias, supporting the theory. How difficult would it be to firmly disprove that theory?
It's far too easy, and without serious drawbacks, to publish studies or theories that promise an easy fix, which gets some people excited.