If you watch the replay of the trap br the Ark WR count the number of men on offense, I believe you'll find 12 Ark players. Also, watch the whole series, the trap play was a 5th down.
I believe that the play on which they had 12 men on the field was the second down play. They scored the touchdown on the trapped pass on 4th down, and I don't recall anything about a fifth down. That happened in the Colorado/Missouri game in 1990.