You have a right to a restitution hearing to have the court determine what, if any, recitation you owe. No matter who paid the medical bills, you would be responsible for paying the restitution.
The above answer is for general information only and is based on the information you posted. Every case is fact dependent, so to get a thorough analysis of your situation, you will need to consult face to face with an attorney licensed to practice in the jurisdiction where the incident took place. Do not conclusively rely on any information posted online when deciding what to do about your case.
You are always responsible for the restitution in a criminal case. In fact, if you don't pay, you can have your probation revoked, and you cannot get off probation until the restitution is paid. You may be entitled to a hearing and see that actual damages of the billing, but be careful. If he only requested the medical bills, he may ask for lost wages and they will award it.