What the study says is out of 20k people that had the vaccine or previous infection only 200 got reinfected and nobody died. Yes in the 200 there were more vaccinated but imaging how many people died from the first round of infections. How the people who were sick are much more cautious and wear masks than vaccinated. None of this is adjusted for (ie they don’t ask a sample of the groups a question how often do you wear mask, all they needed to do was ask from 300 people from both groups and you could adjust for risky behaviors and I bet the effect would be much smaller). In any case both vaccine and previous infection provides plenty of protection.