Mold growth in a home is the result of increased trapped water vapor. Water vapor is of course caused by a number of sources including: bathroom fans venting into the attic, cooking, showering, improperly vented dryers etc.
But water entry can happen in an area that you may not think of.
What could your electrical service have to do with mold? If the electrical service into your home is installed incorrectly, (where the weather head is lower than the electrical service attachment point), water can enter the circuit breaker panel and evaporate into the basement. Moving past the obvious fire hazard of water and electricity, this is an overlooked source of water entry into the home. The pictures are numbered in order of how water can enter through the electrical service:
I’m sure that if you are a home inspector, you also noted the over full panel, the double tapping, the spliced wires, as well as the neutrals and grounds under the same lug. The main point is that water entry can come from a number of places, some of them you might not immediately think of.