I can see that happening. The thing to remember is that there is ALWAYS a possible source of ignition. So never assume that just because things are off and not warm, there cant be a spark. Static discharge is common, tools can cause sparks, even things as minute as eddy currents in the metals have been known to ignite volitile vapors.

Hope he recovers quickly, and it should be a reminder to us all that we are working with combustibles.