The American embassy used to be situated in a building directly in front of the Matusita house, and it is said that the legends were all invented and fostered by the American mission so as to prevent people from entering the Matusita house and using it as a site to launch terrorist attacks on the embassy itself (during the late 80s unrest due to the communist Sendero Luminoso).
This version is corroborated by multiple  facts. First, my mother and her coevals heard of the Matusita stories only in the early nineties, and second, as a consular officer herself, she once heard from her peers at the Ministry that the Matusita legends were a product of “Hollywood at its politically finest”.