I have yet to see old ammo be over pressure simply because of its age. IN my experience failures in old ammunition result in FTF or squibs.
The powder in the vast majority of .30-06 ammo was pretty stable stuff. iirc it was made by DOW and is very similar to H-4895.
It seems more likely that round had a double load of powder. Pretty much the same reason a new round would have a catastrophic accident.
Some .30-06 rounds were made specifically for the .30 cal. machine gun. Not sure if it was a higher pressure round than the standard rifle cartridge. If it was that might explain the Garand blowing up.