That's an interesting article. It confirms that the Buffalo/Niagara region of NY did have 25Hz generators, but I wonder how late regular residential loads were actually being supplied at that frequency, and not at 60Hz via converters?
By the way, the book I mentioned at the start is actually on model railroad wiring. This is the third edition, with the first out in 1950, so it's possible that things had changed in those few years as grids were expanded and developed.
I guess there's also the possibility that the generators were only feeding into the 60Hz converters by that time but somebody just got the wrong end of the stick.