I think you handled it very well. You were honest, you got his attention and it sunk in. It had to be stated bluntly, because obviously otherwise he just does not seem to understand his behaviors are HIS. He does not get subtle.
Yes, he is in a defiant stage and so ALL of the adults in his life need to make sure he knows he cannot get away with ANYTHING. It is the loving thing to do. Nip it in the bud now, so it is not when he gets in real trouble you are wondering what to do.
Children NEED this type of direction and attention.. They do not even realize it, but they are just testing.
So keep an eye on him. When he is good, when he keeps it together, when you see him control himself. Mention to him in a positive manner.
"I sure do like how you sat right down." "Thank you for holding my hand while we walk through the store." "Wow, you were a big help getting your jacket and boots on."
"You are a great helper when you carry that bag for me." "I like how you said goodbye to your friends so nicely. " "Nice manners!"
The last thing is for you and your husband to model good behaviors. You are going to feel foolish putting words to it, but your son needs tohe auditory and the visual of behaviors..
You drop and break something. "Oh no! I dropped the glass. How frustrating! I need to get the broom and sweep it. I did not mean to do it, but it was just an accident."
You are running late. "Yikes, I am off of my schedule. I cannot be late. I better move faster. I need your help. Please put your own jacket on and meet me by the front door. I should not have dilly dallied around. I have made myself late."
You forgot to purchase something at the store. "Ugh, I forgot to buy milk at the store! That was the main reason I went. I guess I just forgot. Well I am going to write it down so next time I will not forget.. Not a big deal, we all forget sometimes,"
You are angry because of the weather. "Wow, it is raining? I am so frustrated, I was going to do some work out in the yard. Now my plans have to all be changed. Well there are other things I can do instead, but I am still disappointed and kind of frustrated. "
He needs to see, hear and then see how you all handle these situations. He needs to know "you do not hit or spit at dad when you get upset, because it would hurt dads feelings. Dad would never spit at your son, because it would hurt sons feelings and so son should never spit at a classmate, because it will hurt his feelings. "
"We listen to the teacher, because she needs us to behave at school so we can learn. "
I know it sound like a lot of time, but better to take the time now while he is still young enough to control , rather than later when he is bigger than you.