I believe that you are correct in your calculation, but incorrect in your assumption. You are treating the curve of daily deaths as the thing to be differentia

I believe that you are correct in your calculation, but incorrect in your assumption. You are treating the curve of daily deaths as the thing to be differentiated. They are treating the curve of total deaths as the thing to be differentiated. While the curve of daily deaths certainly would have a negative acceleration, the curve of total deaths is monotonically non-decreasing and therefore the second derivative is always positive but trending towards zero. Like I mentioned above, the only way for total deaths to decrease (making the function not monotonically increasing and therefore capable of having a negative acceleration) would be through errors of accounting.