Why are you bringing facts into the discussion? Our prejudices are not based on facts!
And the party boat is actually between Norway and Denmark, where Denmark is in the EU and already has cheep booze domestically, so the Danes going to Norway don't actually benefit much from Tax-free booze, but for the Norwegians, the price might be 1/2 or 1/3 the regular price, so the Norsemen are having a party!
https://www.dfds.com/en/passenger-ferries/ferry-crossings/ferry-to-norway/copenhagen-oslo