It isn't a conflict of interest. He just has very strong motivation to get good science for ME. A lot of people research something of personal interest. The people least likely to have conflicts of interest over ME research are pwme or their carers. We aren't likely to be sidetracked by career advantages and so on.
They are talking about disclosing personal motivations (which isn't the same as Conflict of Interest). In terms of being transparent about personal perspective, there could be a bigger place for that in research, but it definitely doesn't feel appropriate to have patient-researchers prove that they do have the condition. That would be humiliating and unnecessary.