> seemed dumb to me to cool the interior of your refrigerator by dumping heat into your home, which your AC has to then extract and dump outside.

This doesn't strike me as dumb at all, unless the refrigerator's heat pump is more efficient [1] than the AC. Although it may be, it's not a foregone conclusion, and it stands to reason that a refrigerator would be designed to function better when pumping [2] heat into room temperatures than outdoor temperatures (as opposed to an AC).

Regardless, all heat pumps have to work harder (use more energy and/or run longer) when the temperature differential on either side is worse. You wouldn't be getting something for nothing by moving a fridge's hot side to a hotter outdoor location.

[1] Overall, including maintenance/replacement cost due to longer run-time

[2] or dumping, though "dump" suggest something more passive than what I believe is going on