I can't really ad to what the others have said except for the following.
Having been the other couple in a situation like this with newbies that didn't adequately explain their limitations before we got to the play room, I can explain what happened here.
When you returned to the room and saw what was happening, my guess is, your feelings about it were plainly visible by the expression on your face. When that happens to us we immediately get dressed and exit the situation as fast as possible in an attempt to avoid the drama that is obviously coming. So, while your girl apparently went further than you had agreed, based on what you have said here, the other couple is not to blame in the least, as you didn't tell them what your rules were, so they had no way of knowing that they were breaking them. Furthermore, you said,
If I were the other couple and heard you ask that I would have assumed we were good to go all the way if your girl friend agreed.
I would also argue that after you asked that question, your girl friend may have been under the same impression. In other words, she may very well have thought after you asked that question that you would approve of her doing what she did.