What Should I Have Done?

Today I went to lunch with a group of my girlfriends and their children. We love to go to Barro's (a local pizza chain) where there is a great play area for all of our kids to run around while we chat.
While we were talking, a dad showed up with his two boys who looked to be about ages three and four. They ate their pizza and then the boys started playing with each other while the dad read a book. Our children finished up their pizza and started to play in the same area as the boys. Well, things were fine, the kids were playing like kids do. Then, I noticed that one of the little boys was keeping the playhouse door shut, so that our kids couldn't go inside.
I calmly walked over and just said, "Hey, why don't we open the door, so all the kids can play?" I then walked away. Situation solved. I said it sugary sweet and the boy immediately opened the door for the other kids to play.
I wish I could say it stopped there or maybe the dad backed me up and said, "yes, let's share," or something equally supportive. Unfortunately, what happened next has made me feel nervous and worried all day.
The dad looked up from his book and in a very angry voice said, "Cole! Get over here right now!" I looked at the boy to see his reaction and there was this fear in his face that made me feel sick. I've not often seen kids in fear of their parents, but when you see such a look, it's impossible to not feel panic.
The child immediately walked over to his dad and his dad harshly barked, "What's wrong with you?" The boy just stood there and took it. The dad continued, "Sit down!" The boy crawled up into the bench facing his dad and his dad said again, "What's wrong with you?" The boy started to silently cry. The tears were pouring out of his eyes and his dad sat there glaring at him.
I've never been in a situation, to my knowledge, where I've gotten a child in trouble that I thought may result in physical or mental danger for a child. I felt absolutely terrible. I would've taken back my involvement in the whole thing right then if I could've. Sure, the little boy had been teasing the other kids, but did it really matter? Was it worth his being treated like this?
I was stewing, not knowing how to handle the situation when I heard the dad say, "You're going to get it when we get home." At that point, I felt that I had to go over and say something. So, I stood up and walked over to the table and leaned over to the dad and said, "Excuse me. I'm really sorry, I didn't mean for your son to get in trouble." He said, "Don't worry. If I would've seen it, he would've gotten in trouble from me just the same." I continued, "Really, it was no big deal. The kids weren't mad, I'm not mad. There's nothing to be upset about." The dad just continued to glare at his son and said, "Well, he knows better."
I walked back to my booth completely deflated and worried. For all I knew, I had further made the situation worse for this poor child when I was trying to make it better. The dad and boys quickly left and I don't think that the dad had changed his feelings at all. All I can hope is that he perhaps cooled down in the car.
What do you do about situations like this? How could I have made it better other than just not getting involved in the first place? I still feel sick about all of this.
It's also made me realize how careful I need to be when I speak to my own children. It's so easy to crush a child's self esteem with hateful words and looks. Sometimes I speak in haste when I'm angry and I can see it hurts Ryanna's feelings. I always try to apologize and follow up with a hug and a talk, but still. That old phrase, "Sticks and stones will break my bones, but words will never hurt me." Don't buy it. We are all affected by what people say to us whether it's spoken with kindness or malice.
I wonder if that dad realizes the fear his voice brought into the face of his son? I never, EVER want my child to look at me that way. I never want my children to fear me. I never want them to think that I could even contemplate hurting them intentionally. Situations like this serve as a good reminder that our children are relying on us to feel safe. If we can't provide that safe haven for them when they are little, where do they go when they are older? Who fills that void inside them?
Even though my intervention was done with kindness and good intent, I'm left feeling really hollow about the whole thing. From now on, I'm going to let kids work out their own problems unless someone is being hurt. I just could've never forseen a reaction like this and I certainly don't want to see another.