Normally, if you take out Contents Insurance for your possessions in your flat/house, this will cover your personal liability. This will cover your liability in and away from the flat/house, provided that you are proved legally liable.
Your friend would need to claim against the car drivers car Insurance, if the car driver was at fault. Under car Insurance you have liability cover for accidents in which you cause damage to a third party or their property. So your friend could make a claim against the car driver Insurance for injury and any associated costs.