I have a pool heater and an air conditioner, and I'm running both at the same time. They're fifty feet apart, but this thought crosses my mind constantly.
The sticker on the side of the doohickey in the video really gives the whole thing a feeling of "a dude makes these by hand in his garage." I looked up "AC pool heat exchanger" and lo and behold, the same company showed up as the first result:
It's a stainless steel coil that you can put on your A/C and then run water from your pool over it to heat the pool.
https://www.youtube.com/watch?v=J7fB8ul9dZw