From what I just googled around they don't really "speak English" as much as they know all the functional words - in English - to work with ATC. So "good night" is a "standard ATC term".

If the pilot was saying "good night" - as in "you will never see me again, I am ditching this plane and all the passengers into the Indian ocean" - he would have probably chosen words that really meant what he planned.

The news is all about sensationalizing facts to get more viewers.