Many more hot days and no problem, so all is good now.
You can check your cables right away, and see right off the bat if the cruise control has too much tension. The cruise control cable should have roughly the same amount of slack as the throttle cable.
The cable should be able to deflect a tiny bit without moving the throttle plate when you press down on it with your finger. Mine didn't. At rest with the car cold, the cruise control cable was completely taut. The slightest pressure would cause the throttle to open a little. If it does that, you most likely will have the problem under the right conditions. Which would most likely be driving on a hot day, then coming to a stop and having the car idling for a while. The lack of air flowing through the engine compartment will allow the whole compartment to get very hot (perfectly normal condition) and in this case, the cable housing to expand just a slight bit, causing the throttle to be held open.
On a side note, I've thought further into this, and realized that it can't be the actual cable itself expanding, because that wouldn't make sense. If the cable expanded, that wouldn't put more tension on it, it would do the opposite. And anyway, a steel cable would not be prone to changing length under these temperatures. What's expanding is actually the black plastic tubing that the cable rides in, causing the cable to become more taut.