Though you are correct, it is rather time-consuming and energy inefficient to break the O-H bonds in water, especially in the quantity required to support combustion. Based on what I remember from performing an electrolysis experiment for a science fair in middle school, I would estimate that it would take the better part of a day to generate enough Hydrogen to fill a balloon using commonly available household power sources. It is significantly more probable that the guy used butane, which is available at many gas stations as a refill can that costs only a few bucks.

As a former pyromaniac, It is my opinion that the flame (both before and during the explosion), is of the same quality and color of burning butane. Hydrogen tends to burn very rapidly, producing a faint blue, nearly invisible flame. It also makes a popping or "whoosh" sound (which, unfortunately, cannot be heard).

You should probably make sure you know something about what you're talking about before you argue with a Microbiology B.S. student. Maybe it's the wine that's tipping me toward being argumentative, but I'm a little annoyed by some ill-informed guy on the internet calling me an idiot.

EDIT: As someone in this thread noted, it is possible to generate H2 gas by reacting Aluminum foil with HCl (found in the majority of drain cleaners); however, as I stated before, butane is cheap and easily available, and the average individual likely wouldn't know how to generate high concentrations of H2 gas.