Gobblenut I assume they have cut open a few turkey skulls over the years and or x rayed them? No idea why they would assume anything, if you ever hear a scientist talk they don't just go about making claims, can they be wrong of course but the anatomy of a turkey skull is something I would be confident they know well.
I too have seen birds that needed a reminder where I was but those a far less common than the ones that have it figured out, hell if I was listening to most turkey hunters call from the same location for an hour I am pretty sure I could pin point them as well.
It was on THP's youtube channel, you know the scourge of turkey hunting, the same ones who raised some substantial money for turkey research, hate them or not at least they are helping the resource in some fashion.