You’re right! It’s misleading and that’s not fair.
I did some more research and it seems that Selenite is usually more rare than Satin Spar so it tends to be more expensive. 
However, according to the mineral database Mindat.org, the name ‘Selenite’ is mostly synonymous with gypsum, which could be either one (Selenite and Satin Spar ar both gypsum).
It would be interesting to find out what variety the ancient Greeks were talking about when they named Selenite after Selene, the goddess of the Moon!