In fact that statement is not correct. Fungus like candida albicans thrive in an alkaline gut. Ideally, some of the good bacterias produce acids that keep it in check. When the PH of the gut starts getting higher, it is the perfect place for the yeast to turn into its pathogenic form.
But apple cider vinegar is beneficial against candida albicans. People doing ACV enemas usually get a great amount of yeast after them.