I don't think we can resolve the intent of Alberto Masi's letter without asking him personally. As a translator and writer, I often come across a statement that is vague, and have to ask the authors what they meant.
It could be that Alberto Masi thought "Funny Americans, of course that bike was built by my father's company. But if they insist, I'll write a letter. Whatever!" (I get that response a lot from Ernest Csuka when researching an older Singer.) Or it could be that this bike, different from all others, stands out in his memory even after 50 years. Whether his memory is correct, is a different matter. Once again drawing on my experience with Singer, even the actual builder's memory (M. Csuka in this instance) is far from infallible. Fortunately, Singer has excellent records documenting almost every bike ever made! This allows us to then check whether the bike really was built for whomever M. Csuka remembers it having been made.
Be this as it may, I applaud the owner's efforts to find out. More so, I encourage somebody go over there and interview all the players involved. It's not that hard, most of those guys love to talk about their life's work. As has been pointed out on this list, many of the people involved are still around, but won't be much longer.
My magazine, Vintage Bicycle Quarterly, would be very happy to publish an interview with Faliero, Ugo, and/or others. It would be even nicer if we could them show some early bikes made by these craftsmen (or their companies, whichever it may be) in conjunction with the interview. If anybody is planning to do this, contact me, and I'll help if I can. (Also remember, publication in VBQ means that tapes of the original conversation have to be submitted, so we don't publish interviews that never happened...)
VBQ's current focus is on French bikes and randonneuring, because that is where my heart lies. I started the magazine to disseminate information I had accumulated, but for which there wasn't an outlet. (I doubt Bicycling! would publish a 2-hour interview with Ernest Csuka of Cycles Alex Singer!) But this doesn't mean other bikes and makers should not be represented in the pages of VBQ. In fact, I hope to have a story on early, rare Campy parts in a future issue.
Jan Heine, Seattle