K.I.
M.,
First don't get angry because it was brought to your attention.
How would you have known he was doing this if someone did not tell you?
And whether or not it is normal behavior is not the issue.
What matters is you telling him not to do it again.
And when your son was bitten you should have brought it up to the teacher so she could find the source and tell that parent to tell their child to stop biting.
That's how children learn.
Don't make a big drawn out deal about it.
Tell him pushing is wrong and don't do it again.
End of story.
Also he can still be a lovable child and push and bite.
Don't be one of those parents that can't hear anything they deem negative about their child.
No child is all good and no child is all bad.