They weren't played. They were fully aware of it. It's one of the many reasons that they should be hanged for treason.The SnapBack was designed to override vetoes. Rouhani and Co were played. They never thought US could find a loophole and leave the deal and still initiate SnapBack.
The US will succeed with the snapback one way or another. In the worst case scenario, one of the Europeans (perhaps the UK) will activate it on their behalf.