Just a thought- Seems to me that a charge of rifle powder in a pistol cartridge, while not a recommended practice, would not be a disaster. Rifle powder burns slower than pistol powder, and would not create an over pressure situation, just an excessive fire ball and low velocity performance. Kinda of like shooting Fg black powder in your 1851 Colt Navy instead of the proper FFFg.
Maybe somebody with more reloading knowledge can chime in.
I believe Alliant just come out with a warning not to use Blue Dot with some .357 Mag and .41 Mag loads/bullets because they're dangerous? Could be the reloader used the proper charge and was using one of the newly declared dangerous loadings.