The problem is that your action which was meant to be a disciplinarian measure to start with, which it would seem your OH supported, turned into an act of anger, and that's where you cross the line, especially as the cause of it was totally disproportional.
As others have said, if my OH had acted like you did, I too would have been furious with him. It's true that it happens to parents, and yes, I will admit that I have at times discipline my kids in anger (and felt bad about it afterwards), but it's bad enough when a parent does so, much worse when it is a step-parent.
You need to discuss with your OH the limits of your disciplining his kids, but frankly, if you cannot control your anger in such minor misbehaviour, than I think you should avoid it all together. In this instance, the misbehaviour wasn't even directed at your but your OH, so you had even less reason to get involved.
It happened, it's not the end of the world, but you do need to accept you handled the situation very wrongly and provide reassurance to your OH that you understand that it was and that it won't happen again.