Considering that on a commercial airliner the only place a passenger can go other than the main cabin is to the bathroom, why would it be significant that there were people using those "conveniences" when the incident, whatever it proves to really be, began? IMHO I don't see that being a real clue or part of the mystery unless the writers start having everyone suspected of being an Other to blame their absence from the cabin as due to being in the bathroom.

__________________
Things fall apart, the center cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;

--Lines 2-6, "The Second Coming" by Wm. Butler Yeats