Yes, it is normal that the car owner is held financially responsible for the accidents of those that they allow to driver their car. When you give permission to another person to operate your vehicle you have vicarious liability for actions of that driver and thus if they are in an accident you, the car owner, can be held responsible along with the driver.

Insurance normally follows a car first and a driver second as well. This means as the car owner your Liability insurance is primary and if the driver is insured his or her Liability insurance is secondary and would be used if your limits were exceeded. So if your friend was at-fault in an accident than the other party could have placed a claim against your Property Damage Liability coverage.

Instead it appears the other party placed a claim against their own Collision coverage and now their insurance is subrogating with (coming after) your insurance carrier for the monies they paid out on the claim, including the deductible the person paid out on their own.

This is why it is important that you make sure your insurance coverages extend to others that you allow to drive your vehicle since if they did not than you could personally be held responsible, along with the driver, for the damages the driver causes in an accident. Also it is important for those that borrow others cars to drive responsibility and try not to be involved in an accident since it goes against their friend's insurance. In your situation your rates may go up since the claim is on your insurance history now.