"I don't think you can generalize [the study] to everybody, but really for people that have risk factors for severe disease," he says, because veterans tend to be older and have more health conditions."

This is not a controlled study, its comparative across number of reinfections. There can be a correlation between overall health and ability to be reinfected. If your health is poor you will be overall more likely to experience death etc as well as symptomatic Covid infection.