A serology test is just proof of prior infection. It says nothing about the severity and would even count asymptomatic cases. So the study is comparing apples and oranges.

1. Antibody positives are more likely the more severe the case of covid

2. Your point was that people with more severe covid would

> thinks they had COVID-19 and didn’t even bother getting tested

The problem with that theory is that the serology testing in this study was conducted on everybody so whether or not people chose to get tested when they had covid was irrelevant. The fact that perceived infection correlates higher with these symptoms means that these symptoms are more related to someone's self perception of infection than any physical change.