I think it's extremely hard to argue that kids tend to be emotionally immature and especially vicious in this regard. But considering the GP has admitted that in retrospect they find this action to be a dick move I think it's important not to try and generalize immature behavior to all of humanity.
The question of whether humans are more biased towards social or antisocial behavior[1] is a complex one that philosophy has struggled with for a long time without a clear consensus.
1. Often historically framed as whether humans are inherently good or evil.
There's never going to be philosophical consensus on the "good/evil/social/antisocial" debate because the human impulse to self-justify and believe that you're the "good guy" is extremely powerful. Those of us who seek to understand human nature have to proceed without consensus as a goal.
Mao Zedong was able to convince kids and teenagers to have their parents and teachers killed during the Cultural Revolution by convincing them that it was prosocial behavior, and indeed their duty. So the question is fraught with conundrums of the form "humans tend to prosocial/antisocial according to which standard?"