The OP doesn't have absolute proof that god doesn't exist, however it is another piece of data that goes along with the masses of other data which makes the existence of a god so extremely unlikely that we can be unbelievably sure that no god exists.
The reason atheists don't use the word "belief" is because it isn't a belief system (it doesn't matter how many times a theist says it is, it just isn't). It is based upon a scientific approach to a simple question - "is there evidence to prove the existence of a god?" and the pure and simple answer to that question is a resounding "No", the amount of evidence against the existence of a god is huge, and the amount of evidence supporting existence of god is pretty much non-existent! This is not an attempt to be smug, or patronising, it is just how it is, and I make no apology for that (why would I, it is not my doing?).
Since the claim of the existence of god is not backed up with evidence, it is not the job of people who don't believe to prove that god doesn't exist (since this is impossible), but it is the responsibility of the theists to prove, with evidence, that god does exist. If I were to claim that there was an invisible unicorn in my house it would be for me to prove that to everyone, the onus would not be upon others to prove that he doesn't exist. If people told me that there was no evidence for my unicorn, I would be unreasonable to claim that they are being hurtful, because they are correct. If they insulted me, then I would have the right to claim they were being hurtful, but that would be against the MN rules, so people wouldn't do that.
In the words of the great Tim Mincin from his song "The Good Book" (look the song up on YouTube, it is very good).
"If you just close your eyes and block your ears
To the accumulated knowledge of the last two thousand years
Then morally, guess what? You're off the hook
And thank Christ you only have to read one book"