It matters for moving forward. If it seems to be a highly spreadable virus, and a small percentage of the population has contracted it, then a significant redu

It matters for moving forward. If it seems to be a highly spreadable virus, and a small percentage of the population has contracted it, then a significant reduction in the current societal restrictions will cause a spike in new infections, which leads to hospitalizations, ventilators, and deaths. If a large percentage of the population has contracted it, and the results we have seen are due to that, then there is less risk in re-opening things. I can't speak to this study's bearing on that, but it's one good reason to care how much of the population has already contracted the virus.