"Incidentally, the story that Harry Beck based his original map design on the electronic circuit board is a myth. There is indeed a Beck style circuit board design tube map in the archives, but it was apparently a joke that was presented to him long after the tube map had been adopted by London Transport."
That exact phrase pops up a lot (like it gets pasted verbatim around the net) but I've yet to see any evidence to corroborate it's even true. Where as it has been widely reported by a number of independent sources (Beck's family, the Transport for London, etc) that Back's plans were based on circuit diagrams. So I have a hard time believing the 'myth' argument is more trustworthy.
Please also note when they talk about Beck's inspiration they say "circuit diagram" and not "circuit board", like the paragraph you quoted.
As far as my brief research shows, Harry Beck came up with his original tube map design in 1931 (which is actually quite different to what we know it as today btw), while the first printed circuit board was invented in 1936 by Paul Eisler. Thus while it's possible that Harry Beck was inspired by circuit diagrams, it's surely not possible that he was inspired by (printed) circuit boards.
https://tfl.gov.uk/corporate/about-tfl/culture-and-heritage/...