There is no prevention any more than you can prevent any other crime. The video has little context, but I can imagine this attacker spotted the CCW, followed/stalked him towards the store, waited for the right moment and then pounced. Exact same as a criminal who wanted to mug someone.
Awareness buys you time, time buys you options
If the CCW had a little more situational awareness, he may have been able to see him coming and either been able to draw, prevent the immediate takedown, or even get a hand on the firearm to prevent disarm. Manage distance enough to create the half-second of “what the FLOWER are you doing?”. If you are more aware (presuming the attacker looked like he was going to attack) you can keep your distance and maybe even get to store security about some weirdo following you.
But that is a tough call, because make no mistake that was a sneak attack. I’d call it a sucker punch, but its more like a sucker tackle. The CCW is immediately behind the curve and has to struggle to catch up.
From the perspective of preventing this in the first place… Dont look like prey. In this case, the visible firearm was the equivalent to putting on a Rolex and then getting mugged. Make sure if you are carrying concealed that it is concealed.
Appendix carriers have an advantage here, in that it is easier to retain possession of the firearm in front of you than it is beside or even behind you.
Some folks will carry a weak-side “get off me” blade. If you dont have a tool, you will have to fall back to hand-to-hand skills, and this CCW at 60+ years old was at a severe deficit against his attacker.