Uhm. Interesting?

Not sure what to say. It shouldn't be too dangerous, since if the copper overheats, the PVC will collapse before there's any sort of pressure build up. Plus, it doesn't look like you have any valves that would allow a pressure increase to occur.

Not sure how durable it all is, though. Any joints you have that are exposed to the fire are unlikely to last long, unless you used high temp silver solder. If you have calcium in your pool, and get build up in the coil, it can insulate the pipe from the water enough to allow the pipe to over heat. And . . . copper is not especially resistant to combustion gas effects.

But, time will tell.