Atheism and skepticism are not synonymous. One can be an atheist and not a skeptic, and yes, one can be a skeptic without being an atheist. This last part requires some explanation. The key is compartmentalization. One can be a skeptic without being an atheist to the extent that one compartmentalizes one's skepticism, keeping it away from one's religious beliefs.
Compartmentalization is how some excellent scientists permit themselves to be religious believers. They make the decision to restrict their application of the scientific method to matters other than religion. It works the same way with skepticism. One can decide to be skeptical in some matters and not others.
I have known many people over the years who advocate skepticism and skillfully apply the scientific method in their work. However, some of them are downright gullible in their personal lives. It is as if they decide to turn off their brains when they get home. Some even manage to sustain superstitious beliefs, including the belief in gods, without a shred of evidence to support them!
This sort of compartmentalization is not any great accomplishment. We can all do it. For example, I am perfectly capable of watching a horror film without mentally critiquing every attempt to scare me with assorted supernatural entities. I choose to do it in this case because it is fun, and I am generally aware that I am doing it.
For those of us who are both skeptics and atheists, we will tell you that we see little reason to keep skepticism out of the religious domain. We may see atheism as a natural consequence of skepticism, and this is because we allow ourselves to be skeptical in matters of religion.
When skeptics gather, some will inevitably want to extend their skepticism into matters of religion. I would be one of them. And yet, I realize that there will be those who prefer to frame religion as being off limits, somehow immune to skeptical inquiry. I think they are mistaken, but I'm not sure I'd go as far as to accuse them of being false skeptics.
H/T to Friendly Atheist