You're right. I should have clarified my response. The concern over toxic mold has been whipped into a hysteria by trial lawyers and mold remediation companies who claim that certain types of mold are responsible for a variety of ailments - anything from memory impairment to Irritable bowel syndrome. Millions and millions of dollars have been made from the mold hysteria industry.
Mold CAN be a serious problem for people with asthma or specific allergies to mold in question. But the same can be said for peanuts, milk products, grains, dog dander or any other number off things. There is no scientific evidence whatsoever to link mold with 95% of the ailments with which it has been linked.
I would urge the homeowner to be concerned but not to buy into the hysteria. If they tore down every home in America that had mold in the basement, we'd have a lot of homeless people. He should, however, contact the attoreny who did his closing and immediately notify his homeowner's insurance company.