There are no mounting screws/bolts that high up and in that position on the B9, it does look like an impact mark.It's highly unlikely that anything within the TV could cause that.
How is the TV mounted and how can you be 100% sure nothing has hit the screen? I only ask regarding the mounting as it's not impossible that a screw was slightly too long nad has pushed into the panel and impact damage can happen in a split second and not be noticed until later.