Well, actually you can certainly do ETOPS on the '76 with an FMC or a generator inop as I and another poster have observed. Did someone tell you otherwise?
Yes, I did read your post. But I reckon a generator or FMC failure is more critical to ETOPS operation than, in this case, the failure of one of three independent systems, which is what LJ60 was seemingly trying to portray.
Thanks for the clarification nevertheless
In my mind, the crew made the right decision; they had time in their hands to work out the failure and heading home they had also the choice of talking to their own staff. As some others had said, much better than having to do the same thing at an outlying station with much less support.