As it turns out, it appears the root cause of that fire was tied to the battery pack's shoddy build quality. More specifically, Plugin Cars says that:
Reports suggest that the vehicle's battery module had developed some leakage, which in turn damaged the pack's insulation and caused a short circuit that led to the blaze.The investigation determined that the battery cell design was not the problem. But, there were quality problems in the battery pack production process and it did not satisfy the demands of the operating conditions in an automobile.
Significantly more damning, though, is an InterChina report claiming that some of China's battery makers rely on "cheap and inferior equipment" to keep prices in check. The report concluded that the nation's battery industry "lacks competent techniques and processing line equipment to guarantee product consistency between batches of volume production." Ouch.
[Source: Plugin Cars]