IDK, looks like the top of a piston to me. Is the engine behaving badly? Poor fuel economy, oil consumption, noises, etc.? If not then put the plugs back and stop being concerned

 

Typical carbon, the only time to be concerned is when one piston looks WAY different than the others….

 

How does it look compared to the other cylinders to have you concerned?

 

Considering you have 230k+ miles on the '08, unless you have some compression, knocking, etc. problems, it looks fine from the top of the cylinder, doesn't seem to have any contact marks with either the intake or exhaust valves. If your (assuming) boroscope has a lateral view, should take a look at the cylinder wall and see if the cross hatch is still good, or any cylinder skirt wear.