Speculation: The scorch might have been made by radioactivity attendant upon the resurrection.
One of the reasons I did that Twitter feed is that I want the truth to come out, all the truth, so I can scorch the earth.
If the scorch on the Shroud is the result of radiation, it could have been radiation that reconstituted the dead body.
"to burn superficially or slightly, but so as to change the color or injure the texture," early 14c., perhaps an alteration of scorrcnenn "make dry, parch" (c.1200), of obscure origin, perhaps from Old Norse skorpna "to be shriveled," cognate with Old English scrimman "to shrink, dry up." Or perhaps from Old French escorchier "to strip off the skin," from Vulgar Latin excorticare "to flay," from ex- (see ex-) + Latin cortex (genitive corticis) "cork;" but OED finds this not likely. Scorched earth military strategy is 1937, translation of Chinese jiaotu, used against the Japanese in a bid to stem their advance into China.