This method is a little bit different than what I use, this one folds the corner in before rolling down the bag, What I do, even in my chips bag, I roll it down, then fold the corners in, then roll it out once over the folded corners. Maybe that would be easier for you to do to this kind of bags?

It’s because the hand joker card there allows straights and flushes to be made with 4 cards, so the 4 black suited cards make a flush, and the gapped sequence makes a straight, since both hands are made together it counts as straight flush. You can ignore the ace. It can get weirder because you can make a 4 card straight and toss another card unrelated but with the same suit as 3 of the straight cards and it still counts as straight flush.