I also heard from a reliable source that several ME/CFS patients who caught SARS-CoV-2 were actually completely cured of their ME/CFS after the acute infection was over.
Haven't we been hearing similar stories from people with ME who caught a bug, recovered, and then noticed that their ME symptoms disappeared for a couple of weeks? This happened to me early on, when I first took antibiotics for C. Pneumoniae. I felt completely cured of ME for a couple of weeks, and then it all came back. (Of course, repeated use of antibiotics had no effect.)
Presumably while the body is fiercely fighting off coronavirus, it may also clear the other underlying infections you have (eg enteroviruses or herpesviruses) which may be causing your ME/CFS.
That is indeed one possibility, but there's another explanation. The immune response to a limited infection is biphasic. First, the immune system ramps up to defeat the infection, and once the body feels the infection is resolved, the immune system depresses itself into an anti-inflammatory state to facilitate healing. (At least that's what I remember from my long-ago immunology class.) This anti-inflammatory state might temporarily eliminate the ME symptoms just like a shot of a corticosteroid.