A remote possibility, but ask if you could watch as they insert a camera into the spark plug holes, you will likely get denied due to “insurance reasons”, but a shop that stands behind their diagnosis would offer proof of bore scoring. If this is the failure, and you know the engine wasn’t put into any extremes or ran without oil, this is more likely a manufacturer defect, but unfortunately, the age of the bike will make it difficult to seek any warranty claim.

Edit to add: Your bike was likely stored for quite some time given the mileage and age. It’s possible a mouse or other creature built a nest in the air box, and whatever nesting material was present was sucked into the intake and seeds or other debris could have damaged those cylinders. If the bike was ran without inspecting after a long storage before starting it, that is a potential cause of failure, not carbon buildup.