Good for BR. It's likely that the poly version might be from an older stock with the newer version being made of silk.
I don't think it's safe to assume that textile polyester is necessarily always cheaper and inferior to 100% silk. Today's microfibre polyesters are worlds away from their ancestors in the sixties and seventies. Different finishes and blends have eliminated many of the problems with breathability and odor retention that have plagued polyester's reputation.
Silk is a natural fabric, and like all natural fabrics, comes in different grades depending on the cocoon. Lower grade silk may not have the same strength, luster, and washability as higher grade silk. That's one reason why it might come with a dry clean only tag.
I think both fabrics have a role to play in a well-curated wardrobe, but it's never right to mis-label which fabric is in the garment you are purchasing.