The Only Explanation Was... FATE.
When Lenny flicked his wrist, the reason everyone thought that the white flame in his hand had disappeared was because he had become so fast that they could not even see that he had waved his hand.
The best part of it was the fact that the white flames destroyed only the undead.
Even the humans that had been fighting the undead creatures deep within their midst were not affected in the slightest bit.
Not even the heat wave from the attack grazed their skin, and in this manner, the millions of undead creatures, including those that were dead, were immediately turned into ash and dust.
The once chaotic and extremely noisy battlefield had instantly become silent.
Even Father Black, looking through the monitor screen, was left speechless. In fact, everyone watching was left speechless. they had seen as the dots on the screen all disappeared until there was nothing left.