This is an odd comparison in the article. First of all, quick math on 13,000 drives and 1.5PB says the existing Netapp system was probably using the 144gb drives. This system was old -- it wasn't a 6200, it was probably a 6000, definitely legacy ontap, two node. You can't even properly source 144gb spares (for a couple years now..). This probably a smoking system when it was sold though.
In terms of density, you can do 1.5PB usable (assuming a modest 2x total efficiency over raw) in something like 45 16T disks. That's 4U, plus the controllers. Is it as pretty as the flashblade? No. Also not proprietary media. In terms of I/O, you can certainly span more than one controller with NAS. There are several ways to do it. Granted, you may want some extra controllers for more I/O. Like... two. For an extra 6U.
It would have been nice if the Netapp phonecallguy had say something more than "we have revenue." I would also be nice to know what current Netapp the Flashblade went up against.