The difference isn't in individual flaps, it's in the entire animation. There's only a difference in the first two flaps, after that they're identical.
The speeds are different - the right one smoothly goes from stationary to the target speed, while the left one appears to speed up and then slow down again. It's explained further down the article.
Manually scrub through the first few seconds of the video - you’ll see that the start of the animation is different.