Definitely some odd things about it. It also seems to not exactly match other studies that found plant-based diets reduce severity rather than occurrence. Might be asymptomatic/low severity cases that aren't being reported

Edit: actually it does seem to line up with this meta analysis (https://onlinelibrary.wiley.com/doi/abs/10.1002/jmv.28298) but I can't find it in sci hub to compare details