Given the quotation marks, I bet the donor insisted on the wording. It would be much truer, and not a possible violation of the First Amendment, to say “to celebrate all of evolution’s creatures.”
My guess is this: the donor was going to give big bucks to the Museum, but insisted on mentioning God’s creatures as a condition of his donation. The Museum, eager for cash, decided to bite the bullet and add some deity to the exhibit, but put it in quotation marks.
But that’s not good enough for the petulant Professor Ceiling Cat. First of all, it misleads the public in two ways: by giving a scientific imprimatur to the idea that animals are “God’s creatures,” and second, by not really making it plain that the quote was insisted on by the anonymous donor—if that’s the case. I myself didn’t get that when I first saw the sign, so how many people will understand? The lesson they will take away is that creatures were the product of God, and that the Museum endorses that.