Checked this one for you.
Apparently there are 9 cabin attendants (incl pursers) on a 747-combi.
On a night flight, they are allowed some time off, max half at a time.
So if half of them go off at a time, there could be a situation where there are only 4 on duty.
There are 4 galleys (the big one next to select seating zone, 1 at row 25, 1 at row 45 and 1 upstairs) so theoretically every galley should be manned.
But perhaps the FA's were so bored that there were two in one galley, leaving the other unattended.
Or she/he ate something wrong and spent 20 mins on the loo (hence the bad mood upon return...)
Or she/he liked the cockpit crew and went to "entertain" them.
Or...