That is taken out of context. The prior sentence pointed out, "we calculate that the 2020 American population of 330 million people has on average..."
The calculation you reference was done using all people in the US. Just two sentences later they wrote, "... would on average lose about 0.2 y of remaining life ..." You need to compare to the groups of affected people, which is generally not 100% of people in the US.
The calculation I reference is the average remaining lifespan for people who die of COVID-19. The additional context doesn't make any difference, it just provides two additional (different) calculations:
average remaining lifespan across the entire population:
> we calculate that the 2020 American population of 330 million people has on average 45.8 y of remaining life expectancy, totaling 14.9 billion person years.
reduction in remaining lifespan in the 70-89 age group:
> Older individuals ages 70 to 89 y, taking those who die and those who survive together, would on average lose about 0.2 y of remaining life, and younger individuals would lose far less.
I did not include these calculations because they are not comparable to the number to which I was responding.
The calculation you reference was done using all people in the US. Just two sentences later they wrote, "... would on average lose about 0.2 y of remaining life ..." You need to compare to the groups of affected people, which is generally not 100% of people in the US.