java moss is a realtively easy plant to grow its a tough plant that grows quickly in my experience and i know alot of people that would agree so i dont see any reason you should be different. are you sure its java moss?
It appears genuine enough - he has lots of positive feedback.
Your moss may have been "passed it" already before you planted. If the green "bits" do not grow any in the next couple of weeks then I would give up on it personally and buy some more. Sorry.
i place my extra moss in a plastic tub outside shaded from direct sunlight immersed in water it gets a bit frail looking but still grows when placed back in my tank