Well your son is still only 3. He obviously stands out from the other kids in his class. The question is why. How old are the other kids? Are they mainly girls? If he is the youngest kid in the class, or if the class is mainly female - this could/should be expected.
I can definitely tell you that any punishment that you do at home for what he did at school is not only a huge waste of time, but only adds to the problem. Children at his age need immediate consequences. To punish him for something he did hours earlier (and I can guarantee you, he either has no memory of or won't remember tomorrow) will never work.
I do think that you need more information on ADHD. Not to say that he has it. But a child with ADHD can focus (actually hyperfocus) on something they like. A book I recommend a lot because it covers so much ground in an easy to read format is,
"The ADD/ ADHD Answer book," by Susan Ashley.
My guess is that being an only child and being only 3 he is still learning proper behavior. You can help with that at home. Check out the post by specialmom in this link and you will find a ton of ways to help him -
http://www.medhelp.org/posts/Child-Behavior/Anger--frustration-mangement-for-my-5-year-old/show/1410486
Also both you and his teacher need to be aware that it takes about 3 weeks of consistent immediate,reinforcement for a child to change their behavior. If the consistency is lacking, so is the behavioral change. Hopefully, I have covered both sides of the coin for you. If you have any more questions, please post.