The original study has something to say about ingroups/outgroups. It’s not exactly the same thing as the one we are discussing here but still:
Punishment may be also related to in-group–out-group distinctions
(37) because people might retaliate if punished by an out-group member (38). Societies also differ in the extent to which their social structures are governed by in-group–out-group distinctions. For instance, according to some cross-cultural psychologists (15, 39) in “collectivist” societies
many interactions are confined to close-knit social networks, whereas in “individualistic” societies interactions are more permeable across social
groups. Because in our experiment all participants were strangers to one another, people in collectivist societies might be more inclined than people in individualistic societies to perceive other participants as out-group members. Therefore, antisocial punishment might be stronger in collectivist than in individualistic societies. Our evidence is consistent with this possibility because in regressions similar to those of Table 2 antisocial punishment is highly significantly correlated with a widely used societal level measure of individualism-collectivism (15) (table S10).
The original study has something to say about ingroups/outgroups. It’s not exactly the same thing as the one we are discussing here but still: