If it is called a basement, workshop, storage then no protection is required. If it is called a garage then you must comply with R302.6. The code does not reference gas-fueled equipment.
CRC & CBC definitions:
BASEMENT. A story that is not a story above grade plane. (see “Story above grade plane”).
STORY ABOVE GRADE PLANE. Any story having its finished floor surface entirely above grade plane, or in which the finished surface of the floor next above is either of the following:
1. More than 6 feet (1829 mm) above grade plane.
2. More than 12 feet (3658 mm) above the finished ground level at any point.
STORY. That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above.
There is no definition of the word garage found in any code. That's because none is needed. A garage is a space that could accommodate a vehicle. I am seldom confused about whether a space is a garage or not a garage. Sometimes the garage has been disguised. The car door is gone and there is a window wall in it's place but it is a garage none the less. You can usually follow the driveway and find a garage.
Labels do not create conditions....conditions create labels.
Identifying a basement can be a bit trickier but note that a basement is not a description of the use but rather, a story. The story here is that there can be a basement garage, workshop, bedroom, laundry or whatever else one chooses. A determination that because it is called a basement ... not a garage and therefor no protection is required, is wrong.
If definitive proof is absolutely required I suggest that the assessor records be perused. That's where you'll see the words "house and garage"