No, I was thinking of Farnborough.
It was a bit longer ago than I remembered (old age problem!), as the game was switched to Highbury, not the Emirates. It was still officially a Farnborough home game, so that explains the record you've found. And the fact that Arsenal wore their away kit. See http://news.bbc.co.uk/sport1/hi/football/fa_cup/2671825.stm