How did dust get under the screen? You sure your not seeing the bumps in the screen that are there for touch reasons?
Sadly I wish it was one of the spots that are on there but unfortunately it is off the pattern/grid of the "touch-bumps", and beneath the first layer of glass.
Either the scratch was already there and you didn't notice it until you cleaned the screen or there was something very abrasive on your screen or lens cloth.
I'm going to have to agree, most likely there was an abrasive in the cloth.
