Why do i have an italian last name and i'm not italian?

i'm trying to research my dad's ancestry for my family tree and the reason i'm asking about italy is because i have an italian last name and so does both of my grandparents. my last name is bacchiega, so is my dad's and granddad and my grandma's name is golinelli. my dad is afro brazilian and my grandparents were listed as mulattos. i know in brazil there's a large italian population (largest italian population outside of brazil) but the thing is, we're not italians and to my knowledge, we don't have any italian heritage either but i'm not sure. most afro brazilians have portuguese last names. why is this different for my family? also, from what i've been reading about italians in brazil is that they came mostly in the 1800s and were farmers, not slave owners (i don't think). if anybody has any sources, advice or information for me, please share thank you.