You say that the first para of the SEP article include the words "[Zombies] are exactly like us in all physical respects but without conscious experiences". Clearly the 'but' implies that we (ie humans) have conscious experiences. If you consider that to be a hidden assumption, so be it. Others might consider it a matter of fact.
Claims of hidden assumptions can be made in relation to almost anything. Suppose I asked you to imagine a planet that was locally identical in every respect to Earth, except that it was flat. Would you say there was a hidden assumption that the Earth was not flat? If I asked you to imagine a white Volkswagen Beetle that was identical to any other white Volkswagen Beetle except that it had a mind of its own, would you say there was a hidden assumption that white Volkswagen Beetles don't have minds of their own? I am as utterly convinced about my having conscious experience as I am about the Earth not being flat and Herbie being a fiction, so to me there is no hidden assumption in the SEP article. If you are convinced that you are a zombie, then to you the SEP article might seem utterly bigoted nonsense that begs a very important question.