Well, if you want to get needlessly pendantic about it, the part that hurts is the destruction of your tissues. Fire has two ways of bringing that about, chemical change by oxidative reaction (i.e. the fire is consuming your tissues as fuel) and mechanical damage from the heat. Your tissues are chocked full of water and need to get quite hot before the fire will consume them (at normal atmospheric concentrations of oxygen). If you ever get a burn of that type, it's going to be a terrible, terrible burn and will only happen after significant damage of the second type.

The second type is mostly the result of water boiling and exploding the tiny vessels that contain it, e.g skin cells. This is highly dependent on the temperature of the fire. Your alcohol example works because the alcohol burns at a relatively low temperature. It takes a second or two for it to put out enough heat to cause damage, even when it's on the surface of your skin. If you used a higher energy fuel, gasoline for instance, there would still be a delay but due to the much hotter flame temperature, it's going to be a lot shorter. With enough heat, your skin cells act like popcorn kernels.

So all that said, depending on the fuel source (whatever was in the can), it easily could have burned the shit out of his face in that short period, especially delicate tissues like skin on your eyeballs.