In scientific terms, it is impossible to arrive at a definitive account of how the candles light unless one is given access to all the relevant data. In this case, having access to ‘all the relevant data’ would mean having someone demonstrate this supposed ability under properly controlled conditions where observations can be made and hypotheses tested until the working mechanism is found or until the ‘miracle’ hypothesis is determined to be the only one which cannot be eliminated.
If someone is willing to give such a demonstration or demonstrations, then we can begin to evaluate the claim being made. If not, then there is no case to answer. It could be a miracle, but any awareness of the history of such claims suggests that the ‘miracle’ hypothesis is the hypothesis of last resort and least likely to withstand scrutiny.
In philosophical terms, you may want to read up on the philosophy of David Hume (or even just Google on Hume and miracles). Hume identified some difficulties with any ‘miracle’ hypothesis which philosophers and theologians are still discussing to this day.
Also (still on the philosophy) there is an epistemological problem with the ‘miracle’ hypothesis. If you accept the ‘miracle’ hypothesis, such that we are invoking super- or supra-natural explanations and departing from the realm of what may be determined scientifically, then any version which fits the facts is as valid as any other. You can say God is enabling the miracle to happen. I could say invisible telekinetic Martians are doing it. Someone else could say it’s Satan’s work, or that Odin is responsible, or an ancient Indian spirit called Disputed Land Claim who operates from Neptune and also draws crop circles. Since all of these fit the facts, and since none yields to analysis more than any other, they must all be allocated ‘equally likely’ status.
From a purely methodological point of view, please don’t try to tell me that only certain kinds of priests can do this. I’m a magician, and I’ve got books on my shelves with various methods in, some of which date back at least a century. Self-igniting and self-extinguishing candles are nothing new, and even Houdini would have seen plenty of both in his time. I won’t divulge any methods here, because we don’t, but if you want to take up an interest in the art and learn about it, you can find the right books and develop your awareness that not everything that looks miraculous really is.