Selling one's home to "hide a major mold problem" is an interesting solution in this day and age, with a major sensitivity on the part of the public to any mold issues, and an equally hostile climate toward deliberate misrepresentation. In either case, the unsuspecting public has the law on its side in pursuing a claim well after closing.
Chances are the problem, if it exists, will be obvious to potential buyers. If your neighbor is using a Realtor to market his home, the agent will be even more vigilant in checking out any issues that influence the home's marketability. In other words, the problem may solve itself.
As far as I know, the Putnam County Board of Health has no mechanism in place to monitor environmental issues that do not affect the public in general...in other words, that are contained totally within a private residence. And, lastly, if you are mistaken, you could have some legal consequences in broadcasting misinformation. Your best option is to talk to whatever agent he is using and share your suspicions.
Hope that helps, and I applaud your outrage.