Did he even have auto insurance on his "dritbike"? Im willing to bet health insruance never heard it the other way around. Hang in for more answers as I am not sure. Sorry about your son.
My son had a dirt bike accident, went to ER. Who pays the bill health or auto insurance?
If you have medical health insurance then that would pay automatically .. If you have medical included in your coverage on the bike itself, then you can file a claim if need be. Most motorcycle insurance policies disallow any type of high risk sport riding including racing .. unless the policy is a specified sport type policy
You need to look at your motorcycle insurance policy. Look to see if it has medical coverage. If it does use it as your primary insurance and you health insurance as the secondary. If you don't have medical on the motorcycle, then just use your health insurance.