That's a good thing. It's the easiest way to get it off and it's wise to do a very hot burn like that to get rid of any residue that may be left over.
I burnt mine (after drilling vent holes) then sanded it with a flap wheel before painting. The sanding took a fair amount of time which is why, when I build another, I will get the barrel from the ebay supplier listed above. They sell unpainted, unlined drums for about £26.
S.