What is the significance of the chariot that he saw?
Rashi: The cavalry riding on a donkey and a camel are a sign for Paras and Madai.
Radak: The lookout saw a chariot of two cavalry, and also a chariot [led via] a donkey and a chariot [led via] a camel.
Radak citing Targum Yonasan: He saw a chariot of a man, and with him a pair of cavalry.
Malbim: When the time came for the tidings that now Bavel will fall, he saw only two officers who fled Bavel on the night that they killed Belshatzar. They fled to the army of Paras and Madai. They were on a donkey and a camel, like those anxious to flee; they did not delay to find horses.
Why does it say "v'Hikshiv Keshev"?
Rashi: There he will hear his Nevu'ah, like great noise of soldiers.
Radak: He should listen if they are close, if he hears their steps.
Radak: It is as if the fleers informed that via them will come the tidings of the end of Bavel.