That makes no sense to me whatsoever to be honest but I'm no mathematician. Why cant you take X number of people that have it, and Y number of people that have died and Y as a percentage of X is the mortality rate? Forget assumptions and guesswork. This many have it, this many died, thats your number, no?

That percentage is far more in line with WHO to be fair and no where near the 60% which is utterly bonkers.