Not correct. There have been numerous tests done on cooking off rounds outside of a chamber (both by feds and civilian organizations). The results are the same across the board. Heck, the Mythbusters did this as well. But did it in an oven. The only thing that even broke the glass was the .50 BMG.
But he wasn't talking about storing whole rounds in ammo cans that I noticed. He was asking about storing powder in a vacuum.
BP is also more to susceptible exponential compression than smokeless powder and pyrodex (SP?).Black powder must be stored in quantity and sold from fireproof "magazines", by law. True BP has lower ignition temps and is more susceptible to such things as static electricity and impact than modern replacements or smokeless powder. The gun shop I worked for had such a magazine that held a couple dozen cans of BP, about the size of a military foot locker and HEAVY gauge steel, plus a larger one in the warehouse. You didn't want your hand in the way if that lid fell closed, I can tell you that!