This is such a terribly written article for a content farm style website.

Apart from the hilarious sub-heading errors, i.e. "What James Camera is saying?", "What is Submersible Lenses", this writer doesn't bother (or hasn't had the experience) to communicate what is novel about this rig. In fact, it looks like he's a content farmer, who pulled out a podcast interview that Pawel Achtel did with Brett Stanley and just vomited the points out on text.

It's a really annoying feature of modern day news theft.

Anyway, I'll boil the salient details down for folks here, as well as a primer on 3D filming:

1. 3D films need to mimic the vision we get from both eyes. However, you cannot achieve the right distance between two eyes (the interocular distance) by putting two cameras side by side, because the cameras are so big.
2. To solve that, 3D films have long used a mirror rig/beam splitter: A mirror that allows cameras to be placed in an L shape, perpendicular each other, so that the right interocular distance can be achieved.
3. What is novel about Pawel's rig, is that rather than putting the whole L-shaped system into a waterproof housing, he made a custom water-infused housing for the lenses and the mirror rig. This allows for less image distortion.
4. He tested a whole bunch of 1980s Nikon lenses before selected two that were best matched in image quality.

That's about it.