That treasure box comes in different colors in different sets, so they are reusing the mould for it. The G3 mermaid treasure chest is even worse, it has an attachment on the back that looks awkward because it's meant for the mermaid playset and it doesn't attach to any G4 playsets.
They've been reusing a lot of G3 accessories. I'm not sure about the vanity, but I know the piano, the flowerpot, and the tea cart are all from G3.