Crossword Genius

Are they why numbers of people get confused? (7,5)

Ross

I believe the answer is:

crossed lines

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

'why numbers of people get confused?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'are they' is the wordplay.
'are' becomes 'crossed' (crossing is a kind of being).
'they' becomes 'lines' (I can't justify this - if you can you should believe this answer much more).
'crossed'+'lines'='CROSSED LINES'

Can you help me to learn more?

I've seen this clue in The Globe and Mail.
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