Having any codewords that are designed to be used over the PA in the event of a mishap is a pretty poor idea.
Already the pax are aware something is wrong but likely don't understand exactly what... add to that an announcement over the PA they don't understand and it's guaranteed to put the fear of Christ up them - It's not rocket science.
...Time for an SOP review Monarch!
I get really tired of comments like this from ill-informed, probably armchair wannabee pilots. If you have no idea what you are talking about - please don't bother posting!
It's amazing how certain individuals seems to think they know better than established airlines (not just Monarch) who use phrases like this, for exactly the reason why Bealzebub has explained so well.
Nicely handled by the crew.
Well done!