In my opionion, any harm to an animal and is not good unless it is in complete self defense and necessary for that defense (not shooting, when a light kick is enough/stopping harm when the threat is gone). As soon as the child is shown to comprehend that hurting others outside of that is bad, and have no remorse for the animal (not the consequences), they are being "cruel". I do think it is normal for kids to retaliate when hurt. ASPD isn't diagnosed until after 18. I don't know why, but there must be a reason for this. Maybe because cruelty is in more than just ASPD? And somebody can be cruel to specific things, without having a disorder maybe??
cru·el
[ kr əl ]

1.merciless: deliberately and remorselessly causing pain or anguish
2.bringing about pain: bringing about pain and distress