Deep scoring in a cylinder can be the result of a mechanical failure, such as a broken piston ring, a broken circlip, or a loose piston pin. This type of damage could be confined to only one cylinder and the cause is easy to see.
There will be abrasive wear to the valve sterns and guides as well as to the pistons, rings and cylinders. The scoring will not be deep, but will be in the form of a mat finish of very fine score marks covering all the rubbing surfaces. All the cylinders would be affected.
Other factors that could cause a breakdown in the oil film between the piston and cylinder must also be considered, such as cooling-system problems, or blowby due to sticking rings.
A coolant leak can contaminate the engine oil and form sludge in the oil pan. This will further affect cylinder lubrication. Blowby can also contaminate the engine oil, and make the additives less effective.
Misalignment of the connecting rod can cause side thrusts on the piston pin which are transmitted to the circlip. This could break the circlip, or damage the piston. If the circlip breaks, particles could score the piston and cylinder, or jam the piston rings, to eventually produce damage such as that illustrated.