You allude to this, but it's been explained to me that the sourness of sourdough comes from the (wild) bacteria, while the rise of the dough comes from the wild

You allude to this, but it's been explained to me that the sourness of sourdough comes from the (wild) bacteria, while the rise of the dough comes from the wild yeast. When you feed your sourdough starter, you discard most of it and supply fresh flour and water. This sets up ideal conditions for growth. The yeast is faster to grow than the bacteria, so the ratio of yeast to bacteria is higher immediately after feeding. Thus, you can control the sourness of the dough through those feedings and their timing relative to preparing the final bread dough. The microorganisms should be invisible. You just see their effects on the mixture. Your starter is probably good if it doubles in size within a few hours of feeding (due to carbon dioxide production by the yeast). If there's visible mold, that's very bad. The yeast should be strong enough to defeat any stray mold long before it can grow enough to be visible. I would just throw that batch out and start from scratch.