Anyone saying this fire is a natural occurrence is completely deluded. There's no such thing as random in the Universe (shocking to some but true), everything has an inherent reason. A causal force. In this case it appears to be humanity itself.
In short: humans aren't required for fire to exist. Your argument is faulty.
Insulting natives for lighting fires shows complete disrespect and ignorance of the underlying environments, flora and fauna as well as their part in all of it. You aren't advanced and knowledgeable: you're just ignorant, smug, and delusional.
I agree that there seems to be a bit of bias (if not racism) in the OP's point, but there's no denying that the vast majority of fires are created by humans, whether indigenous, farmers, or hikers.
If it's something else, it might need to be hidden even better.