This smells apocryphal to me. Very apocryphal.
Like you don’t need a behavioral psychologist to explain why people are going to prefer putting menunthingies out of the way.
Even back before a mouse, graphical applications (like q-basic) would place their menuthingies at the top, in a header. They had already established a pattern we still largely follow today- the most general menu category goes to the right, the most specific to the left.-
File is stuff relating to the document- opening, closing, savoring; document wide settings, etc, where help is… uh… extremely specific and almost never used.
So you already have this pattern in UC design; applications are already following it because it makes sense. So now, your devs need to place another menu bar somewhere, and they place it at the bottom, so it’d out of the way of everything else, and they follow the pattern.
oh. and NeXTSTEP's came out in '88...