Fans of the so called Golden Age D&D from the 1970s and early 80s sometimes criticizes later era game material for suffering from a need to create too much coherence, explaining much more than is really neccessary in order to run a fun game. The downside of this is of course that it detracts from what is important and even takes away some of the mystery.
While the 1970s sources are clear on the fact that the City of the Gods is a source of technology, it is Ritchie and Arneson's DA3 which introduces the space ship and its crewmembers. Granted, Stephen Rocklin goes all the way back to Supplement II, but even there it is unclear to whether St. Stephen is from space, another dimension or what. The vagueness of the nature of the city makes it more mysterious, leaving room for each player and DM to figure things out for themselves.