Sometimes this happens to me when I am clicking to clear a message regarding my army arriving somewhere, or something that doesn't stop play but does show up on my mapscreen and requires clearing. Just as I hit it, an event will pop up and I end up hitting one of the options.
Of course, this only happens with HUGE events that end up causing unwanted wars, etc.
I feel this warrants going back to the last autosave with no guilt whatsoever...