What do these gears drive?
It's a little difficult to believe this sudden expansion theory. The lubrication film thickness will be really small, say 20-30 thousandths of an inch. Of course, these vary depending on camshaft design, loads, etc. But it's a really thin film. And it would be really difficult to do away with the film completely, even if the oil was suction drained. And to then douse with generous quantities of kerosene.
The camshaft bearing clearance in my petrol Swift engine runs to an upper limit of about 30 thousandths of an inch. For the camshaft to expand that much, depending on whatever the coefficient of thermal expansion of the material used, would mean a really sharp rise in temperature in a really short time. Since you said, you didn't drive around or idled for too long after the incident. And this would be if the camshaft was unable to dissipate any heat, ie completely devoid of oil, and head of coolant etc.
Did they check the bearing clearances for the camshaft? Did you see any wear or scuff marks inside the bearing surface. It would be a good idea to see that the head is opened only in your presence to inspect rest of the damage.