In many, if not all automatic transmissions the pump does not circulate transmission fluid when in Park, even though the torque converter is generating heat. It's very possible to overheat a transmission in Park.

He was probably slipping the clutch.

I think you'll find it's been years if not decades since there was a Camry available with a manual transmission

And that would just wear a bearing/spring system or the clutch, which are all repairs that are far cheaper than the cost of an automatic transmission replacement.

But idling an automatic shouldn’t be a problem. It’s a fluid turbine.