Krebs has since updated his post with confirmation from three independent Ashley Madison users confirming their data was in the leak. It looks like this was the real deal.
Having said that, Ashley Madison has approximately zero credibility, so whatever their agents say is open to intense skepticism.
If you work with external payment gateways sometimes you are provided with this information even if the card processing is done directly on the processor page (you only have access to limited information about the card and the transaction)