I think the first guy (probe on Sprinter floor) was vibration testing the floor/frame ... if there was a bad weld, it would cause a different echo pattern.
The automated outer paint system apparently uses electrically-charged paint (a common practice) ... spray positively-charged paint towards a negatively-charged steel body ... you can see the back of the spray patterns bending in towards the body. Far less wastage ... the paint sprayed ends up on the desired metal.
I designed automotive assembly systems as my first job out of college and had the opportunity to train skilled trades on maintaining the equipment. Automotive plants are full of engineering eye candy. And hard working people.
Always liked the body/drive train marriage systems. Amazing to think that before CAD those systems were designed entirely on the board with blue lead and mylar.