The title seems to suggest that the reason many people haven't been infected yet is because they are immune, and that we are therefore approaching herd immunity

The title seems to suggest that the reason many people haven't been infected yet is because they are immune, and that we are therefore approaching herd immunity. I'd caution against drawing that conclusion until case numbers and R0 start declining. In some places where vaccination campaigns have been aggressive, like Israel, we are starting to see what looks like herd immunity. What this study appears to show is that some of the antibodies against coronaviruses that people already have from the common cold may also fight against SARS-CoV-2. But that may have been the case from day 0 of this pandemic.