That's a really bad translation and infact unheard of.

Mangioni translates to really nothing, 'mangiare' is to eat. Mansion translates to 'Mansione' in italian.

Seems like a GTranslate blooper, unless there is some ancient etimology stuff going on.

EDIT: if i check with google without translate,

'mangioni etimology', i get correctly

'Mangione is an Italian surname meaning someone who eats a lot, from the Italian verb mangiare. The name is common in Italy, primarily in Apulia and Sicily.'