Many creationists don't seem to grasp that as much as they fervently believe in The Creation, it cannot be called scientific. I think what Jesus said about rendering to Caesar that which is Caesar's and to God that which is God's should apply here.
For the same reason, they're shooting themselves in the foot with the Intelligent Design theory by insisting that the Designer was God. This is what people in, for example, the Church of Christ profess when they say they don't even accept "Theistic Evolution."
As I understand it, and I'm sure I'll be vehemently corrected here if I'm mistaken, this hypothetical intelligent designer is an unknown entity. Thus the designer(s) could've been from any extraterrestrial civilization extant at the time.
Yeah, an unknown entity. Sure. That's right (Nudge, wink). Could be anyone. Er, I mean Anyone.