hm, i'm not really sure where to position myself here. i get your point, and i'm also scepetical about this developement, but we can't say for sure what material was used to feed the AI.
"we still draw pics" is what the devs say. that may or may not mean that they created the concept, and that the AI just creates variations to be used all over the game. that woudn't be plagiarism. but as said, we can't really tell if that's the case.
well, now i wonder what the laws on the matter actually are. i sure hope artists are somewhat protected against AI copies of their works. but even if, i'd think it's tedious at best and impossible at worst to enforce such laws.