You missed the point. The hurricane could have veered and hit Houston. The food would then have been mis-positioned to the disadvantage of Houston.
The common knowledge comes into play organizationally with the standard operating procedure that individuals and local authorities store enough food to last for 72 hours until the federal and state authorities can organize larger disaster efforts. We don't have to make this up on the spot, its been this way for years.
When I lived in St. Tammany parish, I stocked up. It was the mayor's plan to use the superdome, where was his 72 hours of food?
Houston, Shreveport, Memphis, etc. are exactly where food should have been pre-positioned to to support disaster recovery in New Orleans. You certainly did not want to move supplies into New Orleans proper, because it was understood that New Orleans would need to be completely evacuated in the face of a Cat 4/5 storm. Those people need to go somewhere where they can be sheltered and fed. If the people aren't in New Orleans, the supplies shouldn't be there either.
Regarding the Mayor's plan, I direct your attention to this FR thread and the actual New Orleans evacuation plan.
The primary means of hurricane evacuation will be personal vehicles. School and municipal buses, government-owned vehicles and vehicles provided by volunteer agencies may be used to provide transportation for individuals who lack transportation and require assistance in evacuating.There was never any intent to feed people at the Superdome. It was a "refuge of last resort" meaning that it was a temporary shelter to be used only until the hurricane itself passed. There's nothing in the plan about what to do if the levees break and people are trapped in the "refuges of last resort."
. . .
Last Resort Refuge
The definition of Last Resort Refuge is a place for persons to be protected from the high winds and heavy rains from the storm. Unlike a shelter, there may be little or no water or food and possibly no utilities. A Last Resort Refuge is intended to provide best available survival protection for the duration of the hurricane only.
. . .
When it is determined that weather conditions permit, rescue teams will be sent into areas designated for Last Resort Refuge to transport evacuees to designated shelters.
. . .