Wow, that story got me curious. At first I thought it was an "Aramaic score" (rather than just Aramaic letters), but after listening to the recording of someone performing it I realized that could not have been the case. Anyway, I still think the recording does not sound like anything that would have been produced in the 1400s. In fact, I would put the sound at something from the 1700s (think J.S. Bach, and make sure to the last few notes at the end). Yes, the score may have been designed for strings rather than organ, but I still don't think that the melody seems quite as old as they're saying.
If I had to make a guess, I would say that the "point" of such inscriptions on the facade would be related to the person responsible for them. If it was a prince, the score could have been a personal favorite of his, or if it was someone of a religious background the score could have been some type of prayer. In either case, I think that there were enough people who were delighted by secret "codes" in art or architecture to make it worth it. The patron would have had to have been interested enough in esoteric knowledge to pay the artist or architect to insert the codes in, and I don't think it would have been done without something of benefit (even if it was intangible).
There was also a code for a musical score inserted into Rosslyn Chapel
in Scotland, and I believe there was a short melody inserted into Da Vinci's Last Supper
as well. So this kind of thing was known to happen.