Sand won’t do anything because the fire is self-oxidizing.
From my understanding the recommendation to have a bucket of sand around when handling lithium batteries is not to put the fire out with it, but to have something to throw the battery into that's not gonna catch fire as well, and then to carry the whole bucket somewhere where the battery can just burn out on its own. Is that wrong?
That's not what they're asking. It's not about how C works, it's about how specific APIs written in C work, which is hard to figure out on your own for anyone who is not familiar with that specific code. You'll have to explain that to any developer coming new into the project expected to work with those APIs, no matter their experience with C.