Is this a legacy test? My guess is that it's the 'time past due' status field, and that the number is so high because that's the amount of time before the card was scheduled to be due again. Since it's coming up now anyway, it might be that that field is selected but in a test type that's not actually using spaced repetition, so it's a random / meaningless value.
If you email us a backup of your flashcard database, or post a screenshot of the statistics for this card in the Card Info screen, we can try to figure out more details from there.