As an Italian, I can tell you this is not true at all.
"Mori" was used mostly in the middle ages to reference the Arabs who invaded certain parts of Spain and Sicily. While in other parts of Europe those were dark times, culture stagnated and there was no technological progress, in Sicily and other parts invaded by Arabs it was a period of great progress. That gave us terms still used in astronomy (zenith, nadir...), most of scientific books that survived from classical times were saved thanks to the "Mori", especially concerning mathematics (church wasn't much interested in saving those). Architecture and arts flourished. It was an enlightened time still seen with reverence. If anything, Mori is one of the few words that references to dark skinned people that has an inherent positive quality.
That said, stupid people can use any word they want in stupid ways, so I cannot exclude you might have heard that, but it's not its common meaning.