All right, good night!

[kgruber]

Sounds like a completely normal response to a "coast out" last VHF transmission, to me.

Pilots are always saying "good morning," "good night."

 

[Norman]

Yes, but: The normal protocol for a hand-off would be to read back the next assigned frequency before saying 'good night'. The casualness of the reply leads me to believe there was something wrong and this was the capt's/FO's way of letting someone know in a subtle way that wouldn't be detected by a hijacker.

Again; speculation.