Yes, that certainly was the wrong powder to be using, there's no doubt about it...
Kees, you'll like this;
In the past I've played around with 1fg Meteor Black Powder (from the '70's) that was made in England as a replacement powder when Dupont had its fire...
Anyway, I've tested this powder in calibers of; .40, .45, .50, .54, and my 28ga smoothy, and have tested it in flintlock as well as in caplocks...
Now one would think that this 1fg would be slow igniting "black powder" - but it's not, it's quick!!! The only draw back to it is that it's "dirty" - however I can get 3 to 5 shots off in a .45 caliber flintlock with it before having to have to swab the barrel,,, and in my Ed Rayl .40 caliber barrel (caplock rifle) I once got 11 shots off (40 grain charge) in a row and I think I could have kept on going a bit more, but it was time to go home...
How anyone could possibly think to do a video and post it using Pyrodex in a flintlock and that "slooooooow" ignition, and to do it over and over,,, well it just puzzles the heck out'a me... But it was entertaining...