The only way I can see those passengers getting from Culver City to El Monte for $45 is on UberX. UberXL would probably have cost them closer to $70.
Considering the time it happened, they probably were drunk and ordered the wrong service.
Who really knows if their story about the driver using their phone to cancel the original ride and request a new ride is true or not. I doubt Uber will refund. They could sue the driver, but unless they can somehow prove the driver told them it would be $150-200, or used their phone to rerequest the 2nd ride (I'm sure he'll deny it), they probably are stuck.
My gut feeling is they were drunk, ordered the wrong service, were oblivious to the price until the driver got there, complained to the driver, reordered the UberBlack, said screw it to the the new price (prob because they didn't want to wait for an UberX, and because they were still drunk) and got home and passed out. Next day, after sobering up, they saw their bill and said oh crap.