Really worried about my sons behaviour

[VixieLaa]

I'm really really concerned about my four year old son.
We have just got back from a birthday party of one of the children from his nursery.
Three times while we were there a child was crying because they had been hurt. Nothing major, just a bump here and a crash there, none of which was anything to do with my son. But every time this happened and a child started crying, my son would come straight over to me and say 'mummy I hurt him, I've been bad'.
First of all he was not involved in any of the incidents whatsoever, I was watching him. Secondly I have no idea where he's got this 'I've been bad' thing from as we never use that expression. But that aside I'm really concerned about him thinking everytime anyone is hurt that he did it. And instantly admits to hurting the child, when it was nothing to do with him.
Yes he crashes about the place and gets silly, he's four after all, but he is not a spiteful child at all. Hes a really sweet little boy, and I'm actually really getting concerned. We've all taught him he must say sorry if he hurts anyone, which he always does.
He is definately the kind of child who doesn't grizzle about things, he doesn't have a screaming fit everytime he falls over or hurts himself. So I assumed at nursery it's always him who has to say sorry when him and other children bash heads or both trip over each other. We've had our fair share of incident forms to fill in, and I thought most likely because he doesn't burst into tears instantly like a lot of the children there. Hence why it's always him apologising, but after today I'm really worried, because he's instantly announcing it was him who hurt whoever is crying! I know he's said he did it quite a few times when playing with his cousins, when anyone cries. But I've just said no it's ok it wasn't you (if it wasn't obviously)
We left the party early as he was not happy, he wanted to come home, he looked so sad. It absolutely broke my heart. I tried to explain to him he didn't do anything at all, but he didn't seem to understand.
Sorry for long message, I'm just really concerned about this.
Any advice is welcome
P.s. Am speaking to nursery tomorrow, not quite sure what to say yet

[VioletBam]

I wouldn;t worry too much OP. It sounds as if he is sometimes simply not aware when he HAS hurt someone and so is making sure about it.

Is he often being told to apologise for hurting others at school?