Well, I humbly disagree.The article answers the questions.
Water can contain much less oxygen than air.
And as I said, it depends on the water/air ratio.
If the roots are misted throughout, they will be wet throughout.
The water forms a barrier, oxygen is only taken up from the water, which as the article says contains much less than the air.
You have a very good water supply with the continuously wet roots, but have less air at the roots.
As the article says, it is a jing and jang with water and air at the roots.
The water does not form a barrier, its a conduit. A better one than an inert substance like rock wool or coco.
And I can raise the DO concentration much higher than anything approaching being spoken about in the paper. The paper only tangentially applies to this grow.