I used to avoid going to the parents-in-law’s house for precisely this reason. They were the sort of people who kept a vast array of pills and potions (plus an equal number of dietary superstitions) and weren’t shy about handing out dietary advice. It’s bloody irritating, especially when you have to just sit and nod politely.
The examples you’ve provided are possible. Size of shrimp could vary and therefore it’s subjective when to call it a prawn. Same with fries/chips. It is not correct to call a tail an ass.
I think ‘pigu’ translates more accurately as ‘bottom’ or ‘hindquarters’ rather than ‘ass[hole]’. So it’s maybe anatomically correct simply by virtue of being inexact, if you get my meaning.
Anyway, chickens don’t have an asshole as such, do they? It’s more a sort of general-purpose orifice.