I see someeone has just answered but I'll leave msg as is.
The idea is to create an oil reservoir by drilling a dimple or hole on the front of the piston usually aligning with the bridge (or bridges) of the exhaust port (which are naturally heated by exhaust gas & have a bad heat path to cool them). I would only bother on an engine that was prone to seizing at this point. In the bad old days when bridges were first introduced this was not too uncommon, but I don’t believe this to be a kdx flaw, mainly ‘cause the kdx doesn’t have a thin central bridge.
Feel free to shoot me down if you know better.