[PowderMonkey]

"but the quart bottle of fuel he was pouring instead burst into flames. "

Sounds like somebody poured fuel onto an open flame, with predictable results. In this case, I'd wager the flame was either light blue and difficult to see in ambient light, or perfectly clear like burning high grade alcohol. Giving, thereby, the impression that no flame was present.

[Second Amendment First]

That is the case, the flame may not be visible leading one to believe it is out. As with all fire related items, caution should be used, but one simple error in judgement can be catastrophic.