When you strike a stickman with lightning, a large area fills up with lightning. Then the stickman's head lights on fire. Is this a bug, or is it supposed to happen?
I cannot replicate, do you have a save of it happening?
Yes...
https://powdertoy.co.uk/Browse/View.html?ID=1084714
Type in "forcandunc" on TPT (its a tag)
There is a very simple explination, stickman will emit whatever he dies by. So if he dies by lightning he spews lightning, and fire makes fire.