I'm not taking the exact 75% number here in the following - but close, and I will do some hasty approximations.
Current total cases (maybe off by some hours) is 80,894.
80894 is 20.2% of 400000.
400000 - 80000 = 320000.
So yes, given the article's premises 320000 is pretty much on the optimistic side for humanity.
on edit: but once again my math is probably off somewhere so correct it if you see some glaring error in my reasoning. Also note these numbers are for China, of course.
"if 50% to 75% of cases are asymptomatic that means 25% to 50% are symptomatic."
then I go ahead and choose a number (400000) which is on the optimistic end of this range - 80894 is 20.2% of 400000 - I believe that is quite clear, if 80894 is 20.2% of 400000 and 80894 is the amount of total cases counted in China (no longer the case) then I am assuming 79.8% people asymptomatic that have not been counted! (although of course I did some simplifying of things around so my percentages and numbers are not exact, but I think given the linked article slightly under 320000 people being asymptomatic and 80894 being symptomatic is a very optimistic take)
what number do you want to assume is not counted? millions? I assume that from your earlier post but that does not follow from the 50% to 75% cases are asymptomatic.
Obviously if 50% to 75% are asymptomatic and you had 1 million people infected all together (symptomatic and asymptomatic) that would mean you needed to have at least 250000 (25% of a million) to 500000 (50% of a million) people symptomatic. But we don't have those numbers symptomatic, we have slightly under 81000.
Wuhan (the city, not even the entire province of Hubei) has 11 million people. Given what we know now about how virulently and covertly COVID-19 spreads and how (relatively late) Wuhan went into lockdown, how do you feel about that number?