He tells you where the numbers come from, he did a brute force simulation to cycle through all possible card combinations -- it took the computer 72 days and confirmed by another person doing independent work. I don't think there is a better way to determine the edge then to calculate all possible outcomes.

2% of on the main game with perfect strategy doesn't seem like much, but 8.5% on the bonus bet seems like a pretty big house edge to me. (I wouldn't play this game).

I'm guessing that like Let it Ride and Caribbean Stud most players are playing the bonus bet.

Also keep in mind that a slight change in the pay table could probably provide significantly more edge to the house.