The stone is noticeably heavy and hard, and - as you observed - the polish is a bit brighter than one would expect for the usual varieties of serpentine used to imitate jade. However, some serpentines have a hardness around 6 (higher than jade), which would account for the polish.
Dye was my first thought, too, but loupe examination doesn't show typical traces of dye - the green coloring looks natural.

So...further bulletins as events warrant, I guess.