Malbim: Katzin is one who stands at the end of the camp due to his importance or attribute of strength, wealth or Chachmah, even if he is not a ruler, like "Simlah Lecha Katzin Tihyeh Lanu" (Yeshayah 3:6). Now they did not discuss his reward after the war, just that now he will be a Katzin, for he is strongest. They said "Nilchamnu", for they are all equal, just he is at the end.