I might know what is it exactly.. Its the backlight goin thru, my iPhone has a tiny light dot on the top right of the screen, but its just above the screen..

So the case might be this, the drop opens the tiny hole into a bigger one.. Hence the backlight go thru and atfecting you top right's corner display..

I may be right.. Who knows?

If what i said is really the case, then he should not be worry about it unless he plans to sell it?