It was faked to fool people. It is not a 767 Vg diagram. What weight and altitude is the Vg diagram for? Right, it is a fake diargram made up to fool people, done by a conspracy theoriests on 911. He took a generic Vg diagram and place a new axis on, the scale is off.
A generic Vg diagram was plagiarized and photo-shopped to support some conspiracy theory a plane can't go faster than Vmo, or Vd.
The generic Vg diagram was from this web site -
http://www.free-online-private-pilot-ground-school.com/Load_factors.html
The link you supplied confirms the Vg diagram is fake.
http://www.biggles-software.com/software/757_tech/flight_instruments/_popup_for_40_vmo_mmo.htm
Boeing airplanes are certified to this rule. Therefore, intentional exceeding of Vmo/Mmo is not permitted in normal operations. Exceeding Vmo/Mmo can pose a threat to exceeding design structural integrity and design stability & control criteria of the airplane. At speeds less than Vmo/Mmo the airplane’s flight characteristics have been confirmed by flight testing to meet FAR requirements. At speeds in excess of Vmo/Mmo, however, normal airplane handling characteristics are not assured.
The fake Vg diagram has "structural failure" to the right, not exactly the Boeing official words, "normal airplane handling characteristics are not assured". Don't be fooled by the conspiracy theorists trying to make up false claims.