In this article, the concept of working memory accounts for not consciousness but the accessibility, stability and reportability of certain contents.
For example, when I am reading very carefully, I may not be concentrating on the ambient sounds, my bodily position, my peripheral vision, and the environment of the room. These contents may not have to be retained in working memory in any way as relevant information for the current activity. Nevertheless, it does not necessarily follow that these are unconscious in nature. They can be part of the background of consciousness.
Hence, there is the danger that the author assumes "being available for cognitive manipulation or verbal report" to be synonymous with "being conscious." This is quite an assumption and not one arrived at from the working memory model.