Honestly, when they filmed all of this, I don’t think it was originally meant to be Mustafar.
But you can come up with some Watsonian answer for it regardless. Maybe the cultists put it in the forest for some religious purpose.
Apparently it was always meant to be Mustafar. (The opening section of this script looks like it was somehow actually ripped from the real one.)
This version of the script is just based off the final film. Not earlier drafts. For example, there seems to be no deleted scenes in this script, like the deleted Oracle scene, or Kylo interrogating Chewie.
Anyway, not really important at this point.