It is important to recognize physical forces in the world when we are working our magic so that we do not run around like raving lunatics, thinking every natural force is a gift from the gods or a manifestation of our power.
Hands tremble, this results in wavering flames. This could be as subtle as the pulse of your heartbeat resulting in a barely perceptible waver of fingers or limb. Further, the longer you maintain a stance with your focus you may build up lactic acid or other such strains that result in a further wobble and thus turn into the waver of the flame.
Even beyond this, there are minute forces at play that could have incredibly minor impacts by themselves but ad up as a a whole.
Gravity (anything with Mass possesses gravity, even your hand). Drafts from a window or poorly insulated wall/roof that are too slight to be felt on the skin but might stir a candle flame (it takes a LOT more force to make your curtains or wall hangings shift than it does to make a flame waver).
It can be the improved burn rate as the wick and wax reached a certain heat.
It could have been the release of gases from the wax.
It could have even been your breathing.
Etc. etc. I could go on, but I won't bore you further. I've yet to experience any tangible proof of any kinesis ability that could not be explained.
Don't get me wrong though, I'd love to see it.