I was wondering about this too, as this was a really extreme case of what looked to be mostly plucking combined with a little molting...And honestly (didn't want to say anything then), I was really quite surprised that his CAV didn't do at the very least a Fecal Culture/Gram-Stain to rule-out a Fungal/Yeast Infection, which very commonly causes sudden/acute extreme plucking...I think he said that his CAV didn't run any tests and actually mentioned just starting JoJo on an antibiotic, though you certainly don't want to do that without doing at least a Fecal, and I would say that running routine Blood-Work (including a heavy-metal panel, just to be sure) would be wise...I have routine Blood-Work and a Fecal run once a year on all of my guys at their yearly Wellness-Exams, just to be safe and so that I have recent "baseline" blood-work levels to compare to in-case they do happen to become ill...But when a perfectly healthy parrot starts plucking to the extreme like JoJo did, seemingly out of nowhere, most CAV's first do a Fecal and send the culture out to be grown, and then do the gram-stain/microscopy on the spot in the office to look for yeast, bacteria, parasites, etc. And with a parrot who plucks they typically run routine blood-work including a heavy-metal panel and a biochemical panel to rule-out any type of poisoning/toxicity...If JoJo is fine and not showing outward signs/symptoms of being sick at this point then it's not poisoning/toxicity or heavy-metal poisoning, as he'd be very ill by now, but back when he took him to the Vet over a month ago it definitely could have been heavy-metal poisoning or some kind of toxicity without any outward signs of illness, as they hide them so well...And even at this point, over a month since his Vet appointment and since the acute/sudden plucking started, he could still be suffering from a Fungal or Bacterial infection, either internally OR externally, or a parasite, and still not be showing outward signs/symptoms. Depending on what the infection or parasite is they can hide all outward signs/symptoms for months...
Either way I hope JoJo has stopped plucking himself like he was and that he's got all of his feathers growing back-in, because that was a very extreme case of sudden plucking that was very, very heavy...