I really don't understand the confusion here. The syndromes that happen post-infection are never tied absolutely to the infection. They can't be. There are many different causes for such symptoms. So people wanting absolute answers here is a curious wish. Even the doctors who treat these diseases use conjecture. The Mayo Clinic simply provides %s to explain that these syndromes are idiopathic, no cause is assigned, and then it speculates. Yes, doctors and scientists speculate. And it says the majority are caused by infection.
In the case of young athletes in the year 2020, we're seeing some of them come down with the same thing post-Covid. Even though it can't be absolutely ascribed to Covid, the "coincidence" of it all raises alarms. This is normal for doctors working in this field. It's what they do.
Reading the above links on Johnson, it seems to me that doctors are now saying they don't have answers for the questions people have. They don't know what caused it. They can't know. This isn't like Marfan's where a doctor finds a heart abnormality. It's a different beast. The fact that they haven't found any genetic abnormalities and that he was tested before--well, if they don't know now, they will likely never know. BUT, they can guess.
When you're treated for these syndromes, doctors basically say, focus on treatment and ignore the cause. (I only speak from patient experience, and from seeing top specialists around the country. The listing of ailments from Post-Covid infection is so familiar, it's uncanny, for those dealing with these syndromes. No surprises. Textbook.)