A decent charger should shut itself off into a dead short i.e. if pins where shorted well enough.

I suspect here the juice provided enough of a short to not cause the supply to shutdown but enough for a reasonable amount of current to flow through. Effectively a small heater.

5V/1A is only 5W so somewhat unlikely to cause any larger damage. 5W is definitely enough to cause something to melt.

It shouldn't have gone bang or anything though.