Native speakers in the Mother Country say "torch" when they mean "flashlight" and native speakers in the Colonies (USA and Canada) say "flashlight" when they mean "torch". Why?

PS: This question is prompted by my acquisition of the world's coolest flashlight/torch ... which never needs batteries (one shakes a magnet back and forth through a coil to generate electricity which is stored in a capacitor) and never needs a new light bulb (it has an LED instead). Like I said, totally cool!