No. He
DISbelieves in one more God than a Monotheist.
The Monotheist believes in one God (usually 'Yahweh, or 'Allah' or 'The Trinity'). But he disbelieves in all the Roman Gods, the Greek Gods, the Hindu Gods, the Persian Gods, the Aztec Gods, etc, etc. Let's say, for the sake of argument, that our Monotheist disbelieves in 205 'other Gods'. Our Atheist can disbelieve in 206 Gods, one more than our Monotheist disbelieves in.