I had something similar happen at Beauvais years ago - there were two planes on the tarmac when our (Dublin) boarding call was announced.
Myself and the wife walked out with a group who all headed to the nearest aircraft.
Luckily for me the "little voice" in the back of my head was wondering, so when I got to the top of the stairs I asked was this the Dublin plane???
Err no... that one is...
Cue a PA announcement and a hasty exit of about 20 pax who just thought they had got the plum seats!!!
BTW the first and only time the wife was glad I was a bit of an anorak!!