Article is talking about hacking flash-based disks. It has nothing to do with security of the data once you wiped it. Unlike traditional hard drives that require multiple wipes to securely wipe magnetic part of the disk flash doesnt require so many re-writes. Gdisk wipes hard disk (of flash disk) number of times to comply with goverment regulations so I believe that gdisk wipe is secure on flashes just as it is secure on hard disks.
Cheers.