Thanks to Steve Diggins for bringing this to my attention. Here's an excerpt from the story correcting the record, which is here: http://www.themeparkinsider.com/flume/201705/5568/
"This is simply a large-format photostat or brownline of Herb Ryman's original drawing.... Dozens of these were made to pitch the Park to investors and participants."
What I haven't been able to find is if any other reproductions of Ryman's original were made for other pitches leading up to the start of construction at Disneyland. Additional copies in circulation, obviously, would affect the value of piece.
Clearly, this is an impressive piece of Disney memorabilia, but as a Disney fan and someone who covers theme parks for a living, it's maddening to see bad information get such wide coverage.