It simply means that, on one occasion, you got bored of waiting for AB's rubbish server to respond.
Sometimes, when you click on 'Submit', everything can seem to freeze up. Your answer has actually got through, but AB's server is taking for ever to respond. So you click 'Submit' again. AB's server spots that you've posted 2 identical answers, so it deletes one. The next time you check your profile, you'll see that your 'answers deleted' score has gone up by one.
Chris