Assembled PCBs are washed in water at the end of the manufacturing process to remove flux residues - typically a detergent mix followed by a deionised water rinse, with either spray or immersion washing. Outside of a few specialist applications, solvent-based PCB cleaning is obsolete for environmental and safety reasons. Search online for "aqueous PCB cleaning" if you'd like to learn the details.
I am not at all worried about this video. It is perfectly safe to wash PCBs in water or water-based solutions as long as they are properly rinsed in a deionised solution. If they aren't properly rinsed, there will almost certainly be visible mineral stains on the board. I would happily buy a video card that has been cleaned in this manner, assuming that those stains aren't visible. I'd want to lubricate the fan bearings and re-paste the GPU die, but I'd do that to any used card.
I am not at all worried about this video. It is perfectly safe to wash PCBs in water or water-based solutions as long as they are properly rinsed in a deionised solution. If they aren't properly rinsed, there will almost certainly be visible mineral stains on the board. I would happily buy a video card that has been cleaned in this manner, assuming that those stains aren't visible. I'd want to lubricate the fan bearings and re-paste the GPU die, but I'd do that to any used card.