For those who are interested, the little guy is Estevan Martinez, 4'11", 125 pounds out of Clube De Jiu Jitsu Pitbull, Albuquerque, New Mexico. He's also overdue for a promotion in my opinion.
The reason that footage of Mr. Martinez's matches has been making the rounds is that it is so unusual, even in BJJ, to see someone be so dominant against much larger opponents of comparable experience. Mr. Martinez exemplifies the advice I gave earlier - if you are much smaller then you need to make all the other factors not equal in your favor.
I still say that overcoming vastly superior size and strength can be just as challenging in grappling as in striking. I do have some theories as to why Hanzou may have found it less of an issue in BJJ than in Karate ...
1) In order to develop the necessary skill to overcome much larger and stronger opponents, you need to spend the long, hard, painful, discouraging hours actually training live against larger, stronger resisting opponents and generally getting crushed until you develop the skill necessary to counter the size disadvantage. In a striking art, this process can be even more painful, since it involves getting actually beat on by someone bigger. This means you are likely to find fewer women maintaining the course through the process. (It can be done. I know for a fact that I don't hit as hard as Lucia Rijker.)
2) BJJ takes advantage of the fact that most people don't have good instincts for how to handle themselves on the ground. That means big, strong white belts can often be schooled by much smaller blue belts
in the beginning. Once they learn the basics of how not to do stupid stuff on the ground, the big guys become much more challenging to deal with. An average 125 pound purple belt is not at all guaranteed to have an easy time with a 225 pound athletic blue belt. We repost videos of guys like Mr. Martinez because he's remarkable, not because he's typical.