My guess is they just lost track of some of the Amish. After all they have an average of 7 children per family..hahaha.
But more seriously this is a totally flawed conclusion. There are many people out there who have never had Covid….the death rate from Covid for those people is remarkably low.
So to have any valid conclusions we would have to examine the death rate for those who have contracted the disease. And even then this is a unique group with…er…a narrow gene pool, and with group social distancing much different to the rest of society.
My recommendation is watch the movie Witness, with Harrison Ford investigating the Amish, to understand just how isolated these chappies are.