[Isaac Zachary]

1. The car was stationary. Exhaust temps don't heat up that much from idling, or even revving the engine in a stationary vehicle. If you want heat, put a load on the engine.
2. The temperature of the exhaust tubing is going to be somewhat the average between the exhaust temp and ambient temp. I doubt the exhaust is only 280C or so. It is very likely much, much higher.
3. The O2 sensor was the hottest part of the exhaust. It is also the closest object to the catalytic converter. Therefore, the catalytic converter is also the hottest part of the exhaust. I can only be the hottest part of the exhaust if it's working.