That's the page I quoted so I think we are talking about the same bit. I think you are probably right. It is very badly written. If you only look at the title of box 2: 'Post-exertional malaise AND/OR fatigue' you might simply conclude that it means one or the other and thefore post-exertional malaise isn't a requirement. The specific sentance that follows causes the exact same problem again with the optional Or operator. It's only really the second part of that box which properly describes PEM without giving the option for it not to be present:
I think this really highlights what
@alex3619 is saying above about interpretation or operationalization of criteria.
The poor format might be one reason why HHS didn't want to adopt it.