Bewitched/bewitching

Bewitched/bewitching
 

p.117
-He heard Hermione whisper, 'It's bewitched to look like the sky outside, I read about it in Hogwarts: A History.'

They are staring at the ceiling of the Great Hall.

1. If 'it' is empty, referring to the to-clause, then why not bewitching? Something that makes you bewitched (=bewitches you) should be bewitching.

2. If 'it' is not grammatically empty, referring to the hall ceiling, then why not bewitching?

A spell has been cast to make the ceiling look like the real sky, so the ceiling is bewitched. It would be bewitching if its look were something inherent to the ceiling.