In the original Japanese, it says Obake, not Yokai.
I’m not well-informed about this, but from my understanding:
Obake (お化け): Entities that can shapeshift.
Yokai (妖怪): Supernatural beings that are not derived from human origin, such as oni, kappa and tengu.
Yurei (幽霊): Spirits of deceased humans who cannot leave the world due to grudges or hatred toward something or someone.
Yurei and yokai can be categorized as obake if they possess shapeshifting
abilities.