Yeast is a fungus, so the yeast and fungal forms are the same
This is incorrect. Candida is a dimorphic microbe. This means it can change between two different forms. In this case between a benign yeast and pathogenic fungus. In the yeast form the Candida does not cause any harm because it lacks hyphae and pseudohyphae. These are finger-like projections that allow microbes to dig in to harder tissues such as how mold can penetrate wallboard.
The conversion of Candida albicans between these two forms is pH dependent. In an acidic environment the Candida stays as a yeast and causes no harm. The acidic environment also turns off the Candida growth gene preventing candidiasis. The acids that control this are produced by our acid producing Lactobacillus and Bifidus flora. When we kill off the flora, such as with antibiotics, the pH of the tissues where the flora are normally found become alkaline. This turns on the Candida growth gene and promotes hyphae and pseudohyphae formation leading to candidiasis.