Continuity mistake: The wagon, which is full of explosives, is on fire, so Mulan cuts Kahn (the horse) free with her sword and jumps onto Khan. She starts to ride away, while she holds the reins in her left hand and the sword with her right hand, up in the air. The wagon explodes and in the next shot, she still holds the reins in her left hand, though the sword, still in midair in her right hand, is now actually in its sheath, which is always attached to the left side of her belt. Some arrows are missing on the ground as well. Then her sheathed sword lands on the ground beside her. (00:53:45)
Answer: For the reasons stated. He believes him to be a highly competent soldier and trainer. While this opinion is probably influenced by Li Shang being his son, it does prove to be correct, as Li Shang's training is what allows the small group to succeed in battling the Huns.