There are a lot of variables when it comes to insurance. For example is the car garaged/on a driveway? What security does it have? What's your driving history? Who else is driving on the policy? What your NCD level? Where do you live etc etc.
That said it does seem unusually cheap, and someone may have made a mistake. If that's the case, the insurer can do one of two things - they can stand by the quote (you could be lucky) or as is far more likely, they'll requote it properly. It all depends on whether the Underwriter is having a good or bad day....
