How do you know it was a pressurized airliner and not a private or military plane?
Pressure has everything to do with it, the pressure differential between the inside and outside causes strain in the widow and produces the color patterns. Ever see that effect through a plane window on the ground? I don't think so, unless the window has been permanently distorted by a twist in the airframe.
People take pictures through Plexiglas all the time. I take them through my storm doors frequently, without color patterns.
