Unfamiliar with the game, but on 3D animations on 2D games, some times it's how the engine is used.

For example, Castlevania SotN from what I've seen, runs on a 3D environment, but with the camera in a fixed point and the characters moving within the plane of the camera's view. This allows using far less polygons, to be within the limited amount PS1 games could have while having great visuals. This also allowed to have the aforementioned 3D graphics, like from save points and the demon books from the library part of the castle.

Similarly, despite not having 3D graphics in the traditional sense, iirc Hollow Knight uses a similar fixed camera technique as SotN, but added a moving layered background to give the sense of depth.

Some more examples come to mind, but as, again, unfamiliar with Rayman, Idk how much I'd be straying from the topic.