Well it's CGI so there is a multitude of ways to create this.
However, I once did something ALMOST this deep by dollying in from a wide shot to a super close-up - nobody moved a muscle so the only challenge was just getting the smooth focus-pull.
Then, when I had stopped at the close-up of just the eye - I zoomed in (in the editor) on a still of just the eye so that the pupil would engulf the whole frame and leave just all black screen. I did have to use a garbage matte because there were some reflections in the black pupil that still left color and shape blobs. Then once you are zooming in on the still black pupil - you just layer any other video you want over it and adjust it until you like the effect.... Then you just run the whole sequence backwards.
Who knows - maybe they did that clip just like this - but the whole thing really just looks like elaborate CGI to me.