Charging devices, leaving the TV on to fake occupancy as the article suggests.

Also AC is much more efficient if it keeps the room at a stable temperature rather than letting it heat up and then cooling it down again. I never set it that low myself but some hotels don't have a temp setting, that's true

AC might be comparatively more efficient at cooling the room 1 degree rather than 5, that doesn't mean that keeping that temperature for 8 hours will consume less energy than cooling it once you come back in.

If it were really overall more efficient it would be cheaper for the hotel owner to just keep it on all the time, but clearly it's not.

It really varies. Some places have the bare minimum of air conditioning to say they have it, but underbuild the system such that there’s no chance of recovering if you get back during the day while it’s still sunny&hot outside.