If he’s locked in his truck, it would take awhile for them to get to him, and if he points the gun at them and tells them to back off, unless they are really stupid, they back off.
If the account is accurate, he didn't have time to lock himself in his truck. These guys were bad people, who I doubt would have backed off.
The pommel of a knife will smash the side window of a car the same as a spring loaded center punch. From there, you might drop the guy with one shot, or he might have time to get you before you get him.
I've had to deal with road rage down here. People are insane in south Florida. You might argue that the driver would have to be stupid to advance when he sees a pistol aimed at him, but I observe that he is obviously stupid. The acts of cutting someone off, pounding on his truck, and yelling, "nigger, nigger, nigger," are stupid in any state. It is beyond stupid in a state where there are 300,000 carry permits extant. You do not need one to keep a loaded handgun in the console of the truck, either. Then there's the old adage about bringing a knife to a gunfight.
Evidently they were really stupid.