Did you apologise though?
And to answer your question, if I heard a parent being overly harsh on their kids then yes I would and yes I have intervened. I don't like people getting power kicks from controlling kids. I'm not saying you are one of them, but you were very harsh on your son and you set my blood boiling. I was harsh too, for that I apologise. It's not often I see the red mist descend and I don't usually post that harshly.
I'm very strict with my kids and the kids that I am responsible for, I'm known for it. But there is a fine line. I never punish kids more than once and I would never take away a treat for something as trivial as this.
It is psychological abuse if you over discipline, and especially if you take away treats such as Santa and a school disco for a little silliness! I hope you can see that now.
As someone has said, none of us are perfect and we all make mistakes, the cue is to learn from those mistakes. Just because your friend parents one way, doesn't make her way right. You learn from your own childhood, in my case I learnt what NOT to do.
You have to lower your expectations. He sounds like a good kid who is doing his utmost to please, and you are rewarding him which is great - but do allow him to be a child. Children are naughty, that is their nature, some of that naughtiness we choose to ignore, some we pull them up on and some we punish for. You have to set your own guidelines in place and stick to them.
One last question - you said you are only 19, you have a 4yo son (as he's in Reception so he must be) and another poster implied you have an elder daughter - how can this be?