Nope used a revolutionary technique to create it's night scenes, as well as clouds, which I had no idea where CGI!

Also the model of the Jean Jacket UFO is amazing, notice how they modelled the inside of its mouth even though it hard to see inside, so you can juuuust make out what it looks like on the inside without really being able to make it out.

I adore this movie, the way it gives you just enough information about the creature over time to where you slowly piece together how it works just a little too late is a fantastic way to create that feeling of fridge horror.