How does that get to mean...?
Because that's the code that was allocated to it. 'How did that get to mean' is not the correct way to approach decodes. They are what they are.
I've been a professional pilot for 35 years and never seen that one so it's hardly mainstream knowledge and certainly not something a PPL would be expected to know. If you saw it though you'd just look it up.
Was that actually the answer to a question though? If it was I'd bet the other two were so daft they couldn't be right so tis one wins by default.
Can you post the quote in context?