Crossword Genius

Men rob men ruthlessly but this one doesn’t belong (3-6)

Ross

I believe the answer is:

non-member

I'm a little stuck... Click here to teach me more about this clue!

'this one doesn't belong' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'men rob men ruthlessly' is the wordplay.
'men rob men' anagrams to 'NON-MEMBER'.
Though, I'm unsure how this is indicated.

'but' is the link.

Can you help me to learn more?

(Another definition for non-member that I've seen is " One not in a particular organisation".)

I've seen this clue in the Sydney Morning Herald.
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