to learn how to turn like this?
Bear in mind these guys are in a race and therefore on the extreme limit of what they/the bike can do. Trying to emulate this level will lead to you doing what they do all year round - falling off.
The basics of turning fast at low speed include getting the lean on to counter the centrifugal force (yeh yeh, only present in the area in which is is being observed and in the rotating region of observation, and whatever other physics gubbins I HATE... f**k y'all!). The lean you're looking for is to get your shoulder by the mirror - you're not just moving a head, it's got to be the entire body weight. Do this and you'll be amazed at how quickly you can turn at low speeds.
I don't believe the clutch is employed when you are increasing these speeds but the back brake defo is used. He may be using the front brake but that seems like it's asking for trouble and as above - it takes a lot of bike dropping practice to get these things right.
The gyroscopic effect from opening up the throttle would be useful I suppose if you feel you're going over. Pulling the clutch in might help but then you'll lose speed to two of three gyroscopes, increasing only one. If you've an open space and you feel you're going over, I'd say opening the throttle slightly whilst making your position neutral is probably the way to go. But I dunno, I've not tried it.
The downside is tyre warmth at this time of year - don't bother pushing it unless you have confidence in your tyres to grip. The other bike related issue is to consider the type of bike you have. Clip ons do not work properly. A supermoto is the best kind of bike to learn this on.
So really for the basic effect just turn with a lot more lean - move towards the mirrors. You'll see if turns faster and easier at low speeds. Then you can increase the speed and get tight turns at higher speeds. Use the back brake to settle the bike and finely moderate the speed. You will hit the limit if you push it and I suggest if you want to practice this then you either protect yourself and your bike or get a second set of jacket / trousers and a second bike.
There may also be motorcycle gymkhana training going in in your area - the IAM people may also know someone.
If anyone thinks the advice I've given here is bollocks, please correct me as this is only from playing around myself and not proper training.