The financing rate is 0% because the MSRP of the car is slightly inflated. If you pay with cash, you get a cash incentive (e.g. $2000 off), if you pay by financing, you get a similar discount but in the form of a lower nominal interest rate.

Jurisdictions with good legislation require dealers to also show the effective APR, which takes the cash discount into account and is almost always a more reasonable rate.

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Apart from that there could be lots of special circumstances (making a quota, etc.) that could explain the discount if the offer was made to you personally as opposed to being advertised to the public.