The person who told you said that he was worried. I would be concerned based on that. Obviously there is something going on which needs further investigation. It may be harmless and be a comment made out of anger or frustration at not getting needs met but some underlying issue has provoked the comment. I would talk to a health professional about it.
Your grandson might need to talk to someone to assess him and also help him work through his emotions in a healthy way.
A doctor could be a good place to start.
Thank you for your answer. I have recently learned that when my grandson is with his father they play video games, like Black Ops, and other violent games. He also lets him "play" with a BB gun.
Sounds environmental. Perhaps increased supervision/ limits around such games would be appropriate.
There is a lot of info out there about an association between exposure to violent games and antisocial behaviour.
Sounds like the father could be bonding in more constructive ways to his son.
Kids are impressionable. It may be something that passes. Monitor the behaviour and watch for any early warning signs that things may be deteriorating.
There are other medhelp forums which may be better able to answer your question and offer suggestions/ advice.