This shows how much things are different based on where you live. As far as I know there is no such thing as a fire proof or resistant garage requirement where I live. I did my own contracting building our house, had all inspections and have had a couple of remodels that required a permit and inspection. That was never mentioned. I can see where this should be considered even without the requirement. In hindsight, I would have at least given it some thought. At least I have 10 smoke detectors with 3 of them tied our home security system and 3 carbon monoxide detectors.
My shop and rv garage are well detached from the house. The inspector just looked at the framing and electrical and said he was done. It certainly has no fire barriers. Sounds like the OP may have a similar situation. Interesting discussion.