Might be a quack, but I would not put it past the idea that fungi can act in different ways within our bodies, especially if our immune system is weak where it might be more opportunistic rather than non harmful for healthy immune systems.
Paul Offit also has a great book on the other topic of what to look out for when it comes to quackery called "Do You Believe in Magic?" where he talks about Jenny McCarthy and various doctors who tried to support that movement.