As if evolution and evolutionary theory were not already confusing enough, many creationists complicate matters even further by promulgating the mistaken idea that evolution is the same as abiogenesis. One common way this is done is to argue that evolution cannot explain how life began while creationism can and, therefore, creationism is superior to evolution.
Now, the origin of life is certainly an interesting topic, but it is not a part of evolutionary theory. The study of the naturalistic origins of life is called abiogenesis, and while scientists have not developed a clear explanation of how life might have developed from nonliving material, that has no impact on evolution. Even if life did not begin naturally but was started due to the intervention of some divine power, evolution would still stand on the evidence as our best explanation so far for how that life has developed.
Now, it is true that biological evolution and molecular evolution (the basis of naturalistic explanations of abiogenesis) do have some relation and overlap in the sense that molecular change (in genes) is what drives biological evolution. So, it is not necessarily invalid to join the two especially when you consider that it is hard to draw a definitive line between life and non-life.
The important thing to remember is that evolutionary theory is a scientific theory about how life has developed this means that it begins with the premise that life already exists. It makes no claims as to how that life got here. It could have developed naturally through abiogenesis. It could have been started by a divine power. It could have been started by aliens. Whatever the explanation, evolutionary explanations begin to apply once life appears and begins to reproduce.
Another related error made by some creationists is the idea that evolutionary theory cannot explain the origin of the universe while creationism does and, once again, evolution is inferior to creationism. However, the origins of the universe are even further removed from evolutionary theory than is the origin of life. There is some connection in that scientists seek naturalistic explanations for both, but that is simply due to the fact that they are both scientific pursuits and not because of any inherent relationship such that problems with one will undermine the other.
In both instances described above, the creationists spreading this misunderstanding are doing so for one of two reasons. The first possibility is that they simply do not understand the nature of evolutionary theory. In not having a clear idea about what evolution is, they mistakenly include ideas which do not belong. This failure to understand the topic sheds some interesting light on their attempts to critique it, however.
The second possibility is that some creationists do understand what evolution is and do understand that neither the origin of life nor the origin of the universe are really relevant to the truth or validity of evolutionary theory. In such cases, the creationists in question are being consciously and deliberately dishonest with their audience. Perhaps they imagine that by confusing people as to the true nature of evolution, they will be able to gain more support for their own position a position which is, according to them, more in accordance with the will of God and Christian doctrines.