I’ve been detailing for 33 years now and the steps taken in that video were cautious steps making sure to not cause any damage as you never know the true conditions of things on an older car. As mentioned in the video, sometimes cars that are left untouched like this are going to be far less scratched than those that are dry dusted off by the owner over the years.
This car had lots of ground in dirt so the pre-soaking before wiping off is key to prevent new scratches. I might have just foamed the car first and then used a wide, gentle spray, low psi power washer to rinse it off a bit first but their method seemed to work okay too.
The car probably has single stage paint(no clear coat) I assume with it’s age and find that even a mild polish can remove ground in dirt if there aren’t many scratches. They could have tried a clay bar in between washing and polishing steps but the polishing stage would honestly be more effective on ground in dirt anyway. A mild polish and pad used on a random orbital buffer, so not aggressive polishing at all. If there was oxidation or deep scratches, you’d have to use more aggressive compounds/polishes/pads and more polishing stages.
After polishing, then you would apply some sort of wax/sealant/ceramic coating which would provide better protection than it’s ever had. The previous dirt would have “sealed” it a bit but a proper sealant after cleaning would be even better. If this vehicle was left outside all those years, it would have had major paint oxidation and fading and all the rubber pieces etc would be in rough shape.
Old single stage cars are fun to do as it’s unreal how much better they can look with a polish to remove the years of oxidation. If it’s kept clean and out of the sun in the future it will still look great in years to come after polishing and protecting.
Btw-Some old British cars can look okay if you’ve got a detailing guy!