Okay, in the video the guy on the bottom has both his arms locked out on the opponet's single arm.. While you do this the guy on top punches your lights out with their other free hand. WT/WC does not commit both hands to one arm of the attacker. Grade 1 stuff. Basics. Big no no.
A groin shot with the elbow is great here, I would prefer chain punching the groin, that would bring their face to where I can reach it, and then chian punch their face as you roll them off with your hips.
You can still use your hips to roll them off, anyone would do this.
You can also use your chi sau to defend while your on the bottom, whether they punch at you, or try to lock out and arm or choke.
This is just basic anti-grappling the first stuff you learn, chi sau on the ground comes in a little latter.
What you do striking on your feet, you do on the ground. Your defelction on your feet you use on the ground.
As for that old moldy chueng and emin fight, I've seen that video so many times, and heard people say, "see! grappling is the way to go!" Sifu Emin did it!
So.
That was before he developed the anti-grappling. It may have inspired him to create it in the first place, who knows. But, what he did was NOT BJJ. Nowhere near. Just because it's a ground fighting technique doesn't mean they all come from BJJ.
And no, I totally don't see ANY WC/WT concepts or principles in BJJ at all. If anything, these grapplers and BJJ stylists have already defeated you in the head. You already believe there is just no way to keep from being taken to the ground. So, you WILL be taken to the ground in a fight, because you've already decided that outcome.
Another rule and concept of WC/WT: don't anticipate.
Here's some interesting video instructional to Wing Chun concept on the ground.
The guy he's demonstrating on he states was a "long time in Ju-jitsu" or wrestling or whatever. At the end he "grapples" with the guy to demonstrate why this isn't advantageous to you.
Learn this stuff if your a chunner, I thought everyone did this because hubbie teaches this. I didn't know he mixed two masters my first two years of training, or what that ment.