It's not semantics. There is a difference between atheism and non-theism. Atheism is opposed to all religion and no belief in God or gods. Buddhism is a non-theistic religion that employs the use of meditational deities in visualization practice and sadhanas.
Actually, no.
Your definition is for non-religious, not atheist.Atheists do not believe in God. And usually, this is referring to the god as defined by he majority group of theist that the atheist live among. For instance, Western Atheist do not believe in the god of Abraham. The other Western definition of god actually is derived from the Jewish definition based on the claims of the Christian and Muslims. Stating you do not believe in Jesus or that you do not believe in Allah/mohummad as his prophet does not make you an Atheists. However, stating that you do not believe in the Jewish god makes it impossible to accept Jesus or Allah in any logical fasihion.
However, this does not make you areligious. For instance, I don't believe in the Jewish god as an living entity, but I do appreciate the basic concepts of many of the laws of Moses especially those laws called the 10 commandments. I also apprecaiate some of the behavior laws of Jesus, but do not adhere to them strictly due to specific situations.
That is the difference.