If you look at a pinout diagram of an a-mount lens, it shows that there are, among others, "focusing motor power" (so, a non-logic-level power bus), logic power, and logic pins that are (from camera body perspective) logic outputs. If any of these got shorted together, there would be at least a theoretical risk of camera body damage - shorting any ...
Salt water is the most corrosive thing you can do to the electronics inside a DSLR that doesn't involve a vat of strong acid.
Roger Cicala, the founder of lensrentals.com, has posted at least two blog entries regarding teardowns he did of rental cameras returned after having been exposed to salt water without having actually been submerged in it.
You've got the right approach, but given that the electronics were powered up when the camera took it's swim in the sea, I think it's quite unlikely you'll restore function. Probably the best you can hope for, if the camera was wet inside, is to recover the images from the memory card.
It's caused by the camera's [or computer's] auto ISO trying to amplify an almost zero signal to sufficient brightness to become an averagely-bright [mid grey] image. The result is random noise in the resulting signal.
The way to 'fix' it is to hide it by adding more light.