From the paper itself, the TLDR is that those numbers only apply if you're in a gang. The cohort that is 400% more likely to be shot is, according to the paper, 400% more likely compared to non-illicit activity individuals.

> "However, compared with control participants, shooting case participants were significantly more often Hispanic, more frequently working in high-risk occupations1,2, less educated, and had a greater frequency of prior arrest. At the time of shooting, case participants were also significantly more often involved with alcohol and drugs, outdoors, and closer to areas where more Blacks, Hispanics, and unemployed individuals resided. Case participants were also more likely to be located in areas with less income and more illicit drug trafficking (Table 1)."

It's a good argument for better social services, not for restricting non-gang individuals from owning firearms.