It certainly seems like this crossed the line. If not legally than in the context of acceptable play behavior. Although, as in most he said/she said situations, it's almost impossible to know for sure.

I think that this quote from one of the BDSM experts in the article really seemed to sum up the pair of them.....

“In the BDSM world, you would not want to be playing with … well, either of them, frankly.”

If nothing else this situation serves as a reminder that the more intense or advanced the play, the more critical it is to have clear and detailed negotiations about specific activities and limits before hand.

In BDSM play "go slow and get to know your partner" is always great advice. I have dabbled in the past with CNC play but it was always in the context of a committed long term relationship or with a well established Pro Domme with a sterling reputation.