As I was not there I cannot be certain, but consider this. I am prepared for a bit of flak and abuse for this post.
The Captain should not leave the flight deck for all sorts of good reasons, but the modern low coat airline doesn't always select the best leaders for cabin crew. Locos are well staffed by eager young people, but they are not necessarily blessed with age, maturity and experience of dealing with stroppy, argumentative passengers. It may be that the Captain was having to make up
for the inability of the cabin crew to deal with the situation, or the inexperience or the youth, and immaturity of an otherwise able stewardess.
The cheap availability of high volume air transport has not only lowered the "quality" of the passengers.