Todd, your theory that Welles was being confused with Hemingway is not implausible, since it would be easy to confuse the two, both of them being so closely identified with Spain. The article doesn't give the source of the Welles quote, but it would probably be a simple matter to check out it's accuracy if all of Orson Welles's published written works have been accounted for. If it was Hemingway that said it, then I wonder if it was some kind of ulterior political statement.
If it was Welles that said it, then it would be ironic, given that he considered the Chartres cathedral in France to be the greatest work of western civilization. Both buildings are fantastic pieces of architecture. Why would there have been such a difference in his mind between the two? Wouldn't he have recognized Gaudi as a kindred spirit, since La Sagrada Familia is one of the most famous unfinished works in the world? Welles himself left behind half a dozen cinematic La Sagradas.
Here are a couple of interesting Youtube videos about the Gaudi cathedral, especially the computer simulation of what it would look like if it were ever to be finished: