It looks like what they did was pose 3d models, and then use an AI filter to make it look more "realistic"
I have started seeing more and more people who draw sketches or pose models and then just have ai finish the rest of their work. A good example of a 2D artist that does that would be Monkechrome. they don't mention AI being used but when pressed on it they have said they "get help" or "assistance" from AI programs.