وَلَمْ يُسَلِّمُوا، وَذَهَبُوا إِلَى وَجْهِ الْعَدُوِّ
Translation: But the second group does not give salam, and it goes to face the enemy.
The imam’s salam and the followers’ salam are separate. The imam has finished; the second group has not, because it owes another rakah.
The second group returns to guard so that the first group can complete its prayer.