I think they are referring to the occurrence rate of false positives, not that of false negatives. E.g. the page for California lists back through to the Bond Fire, which was contained in 2020. The problem may stem from that the FEMA page lists the incident as a single day https://www.fema.gov/disaster/5385 so this tool doesn't set and end date like it would for https://www.fema.gov/disaster/5382

A similar kind of noise note could probably be made of the "Recent Earthquakes" section. E.g. if you select Indianapolis, IN it includes all the way down to a M2.6 which occurred in NW Tennessee 30 days ago.