I just remembered. Under the game discription, there is a link to his devainart and if you open one of his works and look at the tags, you will see a AI tag.
But don't underestinate the difficulty of work. I tried and making so consistend and detailed images, especialy full body are extremly difficult, becouse the AI always makes some unintented changes, change the face, style a little, blur, error...
Making some simple images is easy, but if you have a detailed character in your mind and you want to generate from different angles for example, the difficulty is high, if you want everything perfect. There is also the lighting and background...
Basicly the more you want to match the image in your imagination with that generated with AI and the more detailed it is, the harder it is to make it (to match and have no error, blur...).