An American was hitch-hiking in Italy

An American was hitch-hiking in Italy and got picked up by an Italian truck driver. The American spoke no Italian but was fluent in Spanish. He and the truck driver (who spoke no English or Spanish) had a lively conversation for two hours: the American was speaking Spanish, and the truck driver was speaking Italian. At the end of the trip, the truck driver asked the American which dialect of Italian he was speaking. What does this tell you about the difference between dialects of Spanish and Italian spoken by these two people as language varieties?