It looked like a honest mistake, but you should have been more careful since you were already reported for similar reason before. I also expected you to be more open to accept your mistake and learn to apologize when you do wrong instead of giving excuses, it will show you take responsibility for your mistake. I would not mind if it was a first offense but i really wanted to see you improve since you were already reported for similar reason before. Thus, i decided to give your 'admin warn' instead.
Make sure you are aware of the number of warns you got, check Staff Discussion board.