I don't disagree that he had experience with multi parasite infestation, as so many things can give those symptomes, but what I don«,t agree with is that what has the plague symptoms is a multi parasite infestation.
It can be more than that. You cannot go saying that the discus plague is a multi parasite infestation, even if those symtoms in his cases were this.
If he would have said something like according to his own experience it is probably a multi parasite infestation, then I could understand but that's not what he says. He says that according to his experience the plague is a multi parasite infestation. that's not true. Not because he has lots of experience with tons of multi parasites infestation that did symptoms like the plague, that does not mean that the plague symtoms is neccessary a multi parasite infestation.
From what I understood, he sort of deny the existance of the plague saying that it is a multi parasites infestation, but I am not english so maybe I misunderstood what he imply by that.