My heart dropped at first because I thought it was a reference to the pier scene from the Half Life 2 tech demo.
https://www.youtube.com/watch?v=4ddJ1OKV63Q&t=350s
But it seems that it's just Abubu's first time experimenting with a 3d background.
Abubu said:
今回はなんか不気味なだけでございます。初の3D背景だし。
Twitter: https://twitter.com/abubu_newnanka/status/1279466956173656064