So far as the process went for remastering the cgi effects the 2K effects were printed out to 35mm film and then scanned at 4K…
Technically, printing the effects shots to film wasn’t actually part of the remastering process. During post-production, some effects shots were finished as film-outs, and some were finished digitally I think. To my knowledge, the film-outs were scanned in 4K, and the digitally finished shots were simply upscaled from 2K.