oh feck, pruni, you are just unfortunate in your friends, I think. Your ds is still VERY small. He has also had, compared to most of these sedate kids, a fair bit of upheaval, in that this is the third (?) move he's had in his life.
Don't condem your ds because of their rxn. I am sure you wouldn't but I know I have been angry with ds, as much because of the shocked reactions of others as my own reaction to his behaviour. I have gotten so utterly sick of being the parent whose kid hit other.
The only other possibility might be working on his expressing his emotions. Will he do that? And do you listen non-judgementally when he does? I think that CAN make a difference. I have worked a lot on this with ds, I think it really helped him.
Your ds isn't one of these other children, thats all. He has his own challenges. So do they. This kind of personality is a good one, I think, just hard to manage in the early years.
I dunno how to express this. I think kids are all of our responsibility and it makes me really and to hear parents feeling criticised or isolated or anything because their kids hit or bite. I don't massively think these things ARE parenting, tbh, I think they are personailty.