Translucent acrylic statues haunt British forest

Agreed. I don’t see plagiarism here.

The basic notion of reflective silhouettes isn’t that remarkable an innovation, so I don’t think it’s reasonable to for one artist (or a random third party) to claim that one iteration trumps all others. The setting is a major element of Mulholland’s work, too; I do think the difference in context adequately distinguishes it.