All NAS means is Network-Attached Storage. It isn't any one particular product. Netapp makes them, EMC makes them, ect. Some of them do have linux or bsd based internals.. but the ones I've used don't allow anyone to log in and get to a console and install/update software. They just provide a web interface themselves that you can go to and configure the allowed methods of connection and whatnot...
Most NAS/SAN solutions are sold as appliances that don't allow you to get inside and tinker with the software.