I hate Pryodex but I have to admit that sometimes it does give higher veloicity than blackpowder in some cases but never at the rate that you found.
I would guess that somehow you got a bad lot of blackpowder.
Pryodex or at least the older stuff did not store very well. If it was over two or three years old it was crap. I am told the newer lots of it is better but I will have to take their word for it. I will never buy it again.
Some of the best blackpowder I ever shot had been stored since the 40s.
A guy gave me a glass container full of FFF that he found in a old barn. We found out later that this once belonged to a guy that used to shoot muzzleloaders in the 40s. He died in 1950.
This was as good or better than any new powder you can buy.