Why does Google's Wing drone have dimples?
These are not actually dimples but shallow bulges. I found a higher-res image online and checked it out. You have to expand the image to full-size and look closely; the angle of sunlight and shadow gives them away:

Similarly, this side view shows that the bumps continue down the side:

The drone is not very large, less than 2 m (6 ft) long. They are not large enough to have significant aerodynamic effect at the speeds the drone flies. Lots of much faster planes have rows of rivet heads which stand out more than these do. They are about the size, shape and spacing one might expect from internal fixings holding a light supporting framework together, maybe there are pop-rivets under there. Another possibility is anchor points for internal equipment or wiring.
To be honest I am disappointed. Dimples are used on golf balls to stabilise flight and have in the past been studied as a way to reduce drag on aircraft. I had hoped at first that work might have been brought back to life. Then again, some cetaceans (whales etc) do have knobbles on their fins, we think to control the boundary layer and reduce drag, but these are just too small and shallow and not organised in the expected way for that.