I saw the video on the website you gave, number 1 to 6 are right, but 7 to 9 are very weird. I can't understand if some one show that to me.
7 we usually use thumb and index finger, just like the number 8 in the website.
8 we usually add middle finger to 7. so we use three fingers to symbol the 8.
9 we usually add ring finger to 8. so we use four fingers to symbol the 9.
BTW, the number 7 in the website, the thumb touch the index finger and the middle finger, it may let people think that you are asking for money.the number 9 in the website, you can use that but get more careful, you need to say 9 with this action because it is means dead usually.and the 8 in Chinese is a good number but is not means lucky. it's means "be rich" because its sound.