They are the same person. You’ll notice she uses the same name as on pixiv for her artstation portfolio page: moshimoshibe.artstation.com

The pixiv profile also has several other socials linked, and her twitter even has a patreon where she takes comission. Those are kinda hard to steal.

ArtStation is like the linkedin of the art industry. People tend to switch to their real names and keep it a bit separate from other social media.