He said he and his father were supposed to take the night bus home to Anhui on Sunday night.
He called police for help about 1 pm.
Police officer Shi Chunhai told China Daily that Qin was crying and on his knees when he arrived at the scene.
"He only started to count the money when we put him in the police car, and it was only 3,700 yuan, of which he'd collected about 3,000 yuan and 700 yuan had been returned by strangers," Shi said.
The police contacted the owners of two cars who picked up Qin's money and drove away after tracking them down from footage on the security cameras at the crossroads. Both car owners returned the money.
Camera footage showed dozens of people, including pedestrians and people driving scooters and cars, stopping to pick up the money, but police refused to describe the incident as a mad cash grab.
"Qin lost control of his money as he ran to pick up the notes as far as 30 to 40 meters away from scene, therefore those who picked up Qin's money were confused as to who the real owner (of the money) was," said Zhao Yi, chief of Xinjing Police Station.
Police asked more than 270 nearby residents, 110 passers-by and 377 people from nearby supermarkets who might be familiar with the situation, to help Qin find his money.
Shanghai police's Sina Weibo also said a person who got out of a passing car to collect money ended up being injured by his own car in the chaos.
Gu Xiaoming, a sociologist at Fudan University, called the behavior of the passers-by a reflection of "an immature personality".
A 9-year-old girl and her father are traveling to 31 major cities across China on foot and by hitchhiking.