Do creationists realize there is no such thing as a default theory in science?

All you say is indeed correct, but that is not the only reason we call creationism pseudo-science. One of the main reasons, if not THE main reason that we call creationism pseudo-science, is that creationism invokes the SUPERNATURAL, which is, of course, prohibited in science. That alone is sufficient to clify creationism as a NON-SCIENCE, not just a pseudo-science.