A reader, John, responded with a correction I thought of adding.
That isn’t a mandolin: it’s a Portuguese guitar (or guitarra portuguesa), a relative of the English guitar, which had been championed (with little success) by Prescott in nineteenth-century England. By contrast, it caught on in Portugal and has never left. The tuning of the guitarra is complex, nothing like that of the mandolin, which is tuned in fifths and has a totally different repertoire. Carlos Goncalves is probably the greatest living practitioner of the guitarra, as well as a composer and interpreter of the music the guitarra seems to have been forever destined for: the fado of Portugal.