I think your reading comprehension is compromised, or that you are biased.
You seem to have missed the money line from the Publication.
“ Overall, our results indicate that mild infection with SARS-CoV-2 induces robust antigen-specific, long-lived humoral immune memory in humans.”
How could you miss that???
Because when they define “long lived” they state it is 7 months, as opposed to the 2 or 3 months from other Coronaviruses.