As in spaghetti and meatballs. To prepare the meatballs, chopped or ground meat must first be somewhat deep-
fried before it is added to a tomato
sauce, where it is allowed to simmer in the
sauce for a while before serving.
Hence the meatball being a "greaseball."
Although meatballs are and have been for centuries, a widely used food preparation for meat among many races all over the world, it is by no means only an Italian food preparation.
To another culture's food that may be more on the bland or less
spicy side, and less complicated in preparation, as in steamed, boiled, broiled or
raw, the combination of a
fried meat added to a spicy tomato
sauce that also includes oil, as in olive oil, in its preparation,
Italian meatballs would stand out as particularly
greasy or oily, to where any perceived ethnic differences would be seen as linked with the choice of food as a "you are what you eat" concept. And that eating complicated and hard to digest foods or "greasy" foods in this case, would have an assumed negative or peculiar affect on a person's mental abilities, outlook, as well as physical attributes, oily skin, greasy hair, to where a racial slur would be invented on the basis of presumed ethnic characteristics stemming from particular food type consumption alone.