I don't see anyway Disney gets a pass on this one.
The guests look like they might be teens. So what?
The guests are not sobbing hysterically. So what?
The guests were not in a *real* emergency. So what?
The phone (probably) worked. There was just no one to answer it. So what?
This is absolutely a clear failure on Disney's part. Yes real world stuff happens there, but they failed the real world response in every way possible - maintenance, training, operations, emergency planning, customer service, incident response. Everything. The situation around the monorails is textbook management failure. All it needs is a tragedy, and it will be a case study.
There is no excuse. I adore the monorails but operate them properly or don't do it at all.