There is really only 1 way to get this message to show up in your log:
[5/20/2016 2:52:13 AM] [DEBUG] [Main Thread] User requested sequence abort...
And that is actually to click on the "Pause Sequence" button and then select "Abort the current Sequence..."
So maybe a very crafty critter got at your mouse...or you were doing some sleep observing? I'm really not sure. But the only way that the above message gets into the log is in the handler for that button. 
Jared