I've heard this from both Americans who have taken a keen interest in Italian cooking and Italians who have encountered them for the first time in the course of a visit to the US. And what one gets in the US
, spaghetti with meatballs the size of golf balls in a fairly liquid sauce is probably American.
However, though Spaghetti with meatballs are rare in Italy there are Italian precursors: I have had spaghetti with tiny meatballs in Puglia, Pino Correnti notes that meatballs were a common addition to feast day pasta sauces
in Sicily, and Ada Boni gives a recipe for pasta with meatballs
in Il Talismano della Felicità.