Any idea what's the root cause and physical phenomenon that this is based on?

From the description I understand that it is nothing like "burn-in" of old CRT's or plasma tubes which results from the same intensity of light being constantly exited off the luminence material which leads to physical wearing-out of the said material.

Also same kind of phenomenon might be possible on OLED displays where bright pixels are worn out, maybe via electomigration of the materials? However this also happens only when the same image is burned to the display for a long time...

But LCD's are a different thing, the colour change in pixels is achieved via polarization change of the material, and in these descriptions the image did not "burn-in" when the same image was shown for a long time but somehow instantly when the device rebooted spontaniously?
And is it so that the image was visible also when the device was turned off?