To be fair, the lounge in Split is not operated by any member airline and is not a Star Gold designated lounge. It is up to the individual airlines to sign up contract lounges in these airports. You may have been spoiled by your home carrier NZ where they make sure any airport they serve you will get a lounge. Try flying UA in Mexico and South America, not having a contract lounge for *G is the norm. So I can see no rules being broken by SK.
The rule is simple. Look out for the Star Gold logo in front of the lounge entry.