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.
--dick