I don't think so. It is more likely Greek with Russian markings meant to fool thimble collectors. It just doesn't have the craftsmanship of pre- or post-Revolution Russian enamelled-silver thimbles. The enamelling is clunky and the metalwork is neither intricate nor well done.
I'm not blaming the seller. I'm sure the seller thinks--believes-- it's a Russian enamelled-silver thimble. What do non-thimble-people know about Russian enamelled-silver thimbles? What do non-thimble-people know about any thimbles? Maybe that they're used for sewing. They always get the finger wrong, plopping them willy-nilly on the index finger. They don't know.