Indeed - and this illustrates yet again that there are few things in safety which are absolutes, and no one thing can be seen in isolation from everything else. Ultimately, people who know much more than we do have to decide whether the benefits of any rule or action are worth the risks, and different people may legitimately reach different conclusions on the same question.

At this level of detail, it's unusual to be able to say Airline X does or did something but Airline Y doesn't or didn't, and one or other of the airlines is or was therefore obviously stupid. Yet there are, of course, plenty of FTers who often assert it, usually on a very slender and incomplete knowledge base, and sometimes stridently so when it has personally inconvenienced them (eg "BA stupidly diverted and I was delayed, when TinPot Airlines didn't").

Back to the original observation, dujardin's post suggested the possibility that AB might be an airline that has a rule of this kind, although of course it might just have been that that crew made a judgement that it was now better to divert.