It's not about macho chivalry - which I guess is what is intended by the Sir Galahad comment. It's about acceptable behaviour in a confined public space. It would be as equally unacceptable if it was two guys.
Whatever the outcome, the police SHOULD have been informed. Many,many female (and male) victims of violent partner abuse, will never report anything. This is not acceptable behavious in an aircraft. Period.
And for the record, if I see anything similar in the street I do get involved.
I still cannot believe what I'm reading on this post, that "oh it's just a domestic, he can beat the sh*t out of her...let's not get involved...it's just a domestic". The ccrew in this instance were wrong, wrong, wrong, wrong and no amount of lame excuses will help.
The police should have been informed, and THEY could judge whether to proceed. As it was, the unqualified ccrew decided to make that judgement themselves. No doubt in order to avoid adverse publicity for Emirates. Shameful.