Explain why the oreads are surprised by the pool’s reaction to narcissus’s death in “the disciple”?

The oreads are surprised about the reaction because The Oreads thought that the pool was sad about losing Narcissus' beauty, but the pool is sad about losing the opportunity to view itself. (it imply that everytime narcissus admire his own beauty at the pool, the pool actually seize it as an opportunity to also see its reflection in narcissus eyes) 

This is a complete adjective clause.