It looks to me, the moisture is being trapped by the engine plastic cover. It is only within the perimeter of the plastic cover this white powdery residue occurs or is present. The car is parked outdoors at the driveway of the house with a car cover.

 

Its just surface corrosion on the aluminum. I've seen it more on people who power wash/clean their engine bay.

 

Correct, that's what I read online that it is not a main concern, just oxidation (surface corrosion). Maybe, the previous owner is a Germaphobes as I found my Jaguar immaculately clean even at 40K + miles, no signs of dust in the interior, I 'll use a magnifying glass next time, maybe my eyes aren't seeing enough .