I would definitely be concerned.
From this distance, it is not possible to determine whether this is a child with delays in social comprehension, who is relating to animals like a much younger child, and getting into problematic peer social situations because he lacks the social language and problem-solving skills to manage them more appropriately, or if this is a case of budding psychopathy.
Either way, now would be the time to evaluate and remediate, before the developmental window for empathy closes in the next few years. Unfortunately, inconsistent or loose behavioral expectations and consequences in the home tend to breed antisocial behavior patterns. I would agree that speaking to his parents depends largely on your relationship with them, but that maintaining consistent environments where you can control them will help to keep you and yours safer, and also provide him with some limited opportunities to learn prosocial skills and develop empathy.
