I am now a bit confused about the meaning of atheist.
I always thought that atheists do not believe in the existence of the creator of the universe (in other words, atheists do not believe that the universe is created). But now it seems atheists are not sure what to believe.
Let me explain to you what I and other atheists mean by the terms we use.
"Theism" is belief God(s). "Theists" are people who have theism. "Atheists" are people who do not have theism (a-theism, literally meaning without theism).
Atheists therefore technically do include those who have not addressed the question as to Gods, though as Yayha has pointed out these people would not know to call themselves atheists or recognize themselves as being atheists, just as people who have never heard of astrology do not recognize their lack of belief in it.
There are different kinds of theists and different kinds of atheists.
Some theists have theism but nothing more. They don't claim to know much about the God they believe in and don't beleive he/she/it/they interferes with human affairs. We call those people "Deists". They include many of the founding fathers of the USA.
Other theists have grouped together into very regimented belief systems with established dogma, holy books, rituals and beliefs that God requires particular things of them. This can be narrow or very wide encompasing much of one's life and society. Islam is a good example of this.
Of the atheists, you have those who lack theism but are not materialists. These people believe in the spiritual but not in Gods. They may believe in ghosts and the like, or they may believe in spiritual forces, such as chi or tao. Taoism and some other far east "religions" are good examples of this, as are some of the new age folks.
Other atheists are materialists, meaning they do not believe in anything beyond matter and energy. This would include most western atheists you hear about.
Some atheists, though they do not believe in gods (and are therefore atheists), find the idea of God plausible enough that they do not dismiss it out of hand. These are the people we call "Agnostics" (literally a-gnostic, without knowledge). Agnostics often also believe that not only do they not know, but that it is impossible to know.
Then you have the atheists who find the idea of Gods so implausible that they do dismiss the idea out of hand. Most of them would reconsider with better evidence, but given what they have seen they view the existence of Gods as likely as there being space aliens monitoring us and walking amongst us, as there being faeries etc. They find it really really implausible. This strong lack of belief can be insulting to theists who don't like to be thought of as outlandish.
Some atheists (though certainly a minority) mock and deride theists as Yahya noted in his OP, the same way they mock and deride those who believe in other claims they find extremely unlikely, like those who tell us about alien abductions, crop circles, etc.
You then have "anti-theists" who not only lack belief in God(s) but find the religions that have been proposed to be distasteful and harmful. These are the atheists such as Christopher Hitchens, Richard Dawkins, and Sam Harris. They are the ones who make the news and who you have probably heard about and associate with the word "atheist".
And that ends our brief discussion of what atheists mean when they use the words they do.
Now returning to your question about if atheists believe the universe is created: Atheists are not one unified group. Atheism just means the lack of theism, nothing more. Theism isn't the only way the universe could have been created, so atheists are quite able to believe the universe was created. They'd just name different agents, such as people in other universes or time loops or whatever.