We're not sure about that conclusion either. One other possibility is that the population currently driving on the roads right now is more prone to accidents than the population currently staying home, and so fatality rates per mile driven have gone up. Perhaps they have older cars without the latest safety features, or their cars have prior accident damage that wasn't fixed, or they skew younger with less driving experience, or they're rushing to get to their jobs, or people are out for joyrides. In that case, fatality rates among drivers staying home have dropped (to zero) and fatality rates among other drivers have probably dropped (less to collide with), but because of Simpson's Paradox overall fatality rates have gone up.

You can't know which is a better explanation unless you have data with more granularity than is typically provided by the press.