What do you think happened?

That would explain the high idle, but not how the cable came out of adjustment by a half inch, and readjusting the cable rectified it. A cable adjustment will not compensate for a vacuum leak.
Follow the linkage/cable/pedal route, make sure there's no binding/ interference anywhere. Check the cable for kinking or binding- a frayed cable can hang up inside the housing, or on the ends... Pay close attention to where the cable enters the cabin and connects to the pedal linkage for anything that may have popped loose or is otherwise out of whack.