A great number of thoughts come to mind on this one.
1) As for the accident, to argue you aren't at fault for this incident is extremely difficult. Sorry if you don't like that but it's a fact.
2) This is a reportable claim to your insurer. Reason being another party suffered damages - The fire dept. The damages they suffered was the cost to respond to the scene, do the clean up, fire prevention or whatever other BS they wrote on the invoice. Your policy requires all such claims be reported to the insurance company, regardless of the dollar amount when it involves a third party.
3) Don't like fire depts charging you for services. Neither do I, which is why I have a particular interest in this area of insurance law. I don't mind telling you I am probably considered one of the leading experts in this area. It's a complex matter. I am sure there were possibly some good legal arguments as to why you didn't have to pay that fire dept bill. Too bad you already paid it but I understand why you did.
As an aside fire departments have become masters at extorting money from tax paying citizens who actually fund the fire dept to begin with. Your house burns down, wait for the fire dept bill of $5000 - $10000 or more. Don't believe me, look into. Even if you die in the fire they still want their bill paid.
4) At a minimum, you should ask your insurer to reimburse you what you paid the fire dept, and now that the claim is on your record you may as well make a claim for the damages to your motorcycle if you have collision coverage.