Potential flaw in the spreadsheet's methodology:

The "Average Mortality Today" column is not meaningful, because it compares confirmed infections in a single day compared to confirmed deaths on the same single day. People confirmed with infections do not necessarily die on the same day they they are confirmed to be infected, so this column can never be accurate. France looks very weird in that column, and I think that might be the reason.

However, the "average mortality overall" column should be more accurate, and yet France is still an unexpected outlier even there. That might indicate a problem where France doesn't have enough early testing, and confirms many of their cases only after they're dead.