It's really a beautiful creation and very well produced. There is heavy use of effects, matte painting, and actual timelapse footage, so even if Terragen had been used it would be heavily augmented. But in fact it looks like most of the work was done in C4D. Which is not a particular specialist in environment production and rendering. I think mostly it just goes to show that passionate people with dedication and artistic vision can create what they want given time, and the tools are often less important to the end result. Terragen could have contributed nicely, but the end result speaks for itself regardless.