ON depends on simple demand and supply (economics 101). Civic still has 200,000 ON (confirmed today). Delivery time for civic is 3 months while that for city is much less. VTi Oriel Pros (which has 200,000 on) is a rare car and is in short supply whereas city is readily available on most showrooms.
The reason city was outselling civic and still had lower on, when you checked rates, was that city was in much more supply (relatively)