That doesn't say that covid is a variant of influenza and towards the end of the July it was believed that aprox 20% of New York City residents had already been infected with covid.

https://www.mountsinai.org/about/newsroom/2020/study-finds-1... It's a discussion of a study published in nature last November.

Despite this cases rose very sharply between October and early January. Your theory doesn't comport with reality as observed.

It says no more the 20% of the population was going to catch it, which was the claim of the comment.