I didn't read that Retro said anything about anti-hammock rules or lay blame for the rock fall on the climbing party.
However, choosing to relax beneath an active climbing party in an exposed supine position is in my opinion not very wise. I am sure many of us have been involved in one of those Keystone Cops style scatterings as everyone is forced to respond to the call of "ROCK!" It's tough challenging enough to evade falling rocks from a standing position or a belay, let alone a hammock.
Secondly, a strung hammock at the base of the cliff cuts off an escape route from any falling debris, gear etc..
I'd call the practice dangerous to one and all.
Fortunately, the injury is limited, and I wish her a fast and complete recovery.