In this comment thread under the post, the artist mentions using Photoshop's generative fill AI feature. They haven't disclosed a work-in-progress for this piece, but they do talk about mentioning AI more overtly if a significant portion of the work was generated. Given that, I assume it's safe to tag the work ai-assisted.
I should note my understanding of this is coming from machine translation of those comments, so if I've somehow grossly misinterpreted the situation due to that, I'm sorry.