I don't know what's actually happening in Germany, but here's one reason one might think that: You can use the number of deaths to reason about the true infect

I don't know what's actually happening in Germany, but here's one reason one might think that: You can use the number of deaths to reason about the true infection rate, independent of the testing strategy. (Until something happens that changes the death rate, like the health system getting overwhelmed.) For example, Germany and France started seeing cases at about the same time and have found about the same number of cases. But France has 10x the deaths. This suggests that Germany has found a larger proportion of their cases, i.e. they've got better test coverage.