In Introduction to Ophthalmic Optics (Meister and Sheedy) this is referred to as Prism by Obliquity, Systems for Ophthalmic Dispensing has a section titled "Induced Prism with Wrap-Around Eyewear"....
The question in the above case is: why didn't that happen? Lab failed to compensate? Lab thought it was already compensated? But under no circumstances should it be off by 6...