I think there is some truth to this, but only to the extent that personality is influenced by culture.
So, for example, people from Latin America, Italy, and Greece tend to be more "huggy" and effusive than people from Germany, Norway, or the UK.
I also think that some of those "ethnic traits" occur in lots of different cultures, but each culture claims it to itself. Thus your example of "Latin temper" and "Irish temper."
My mother, who was born in Italy, used to joke about "Italian time." (If something was supposed to happen in 20 minutes, maybe it would happen after an hour.) But I have since learned that this "trait" gets pinned to lots of other cultures as well. I suspect that it is rooted in agrarian cultures where people don't need clocks.
I would be surprised if any of this were genetic. Although, in recent years we are discovering that genetics is a lot more weird and complicated than people thought, so who knows!
