Searching an object in a collection via lambda

https://www.youtube.com/watch?v=K1xrlc32Tmw&list=PLJUoF2h8Z-brW94dTZ-ZIOhjFq90_lt5K&index=9

4:25 adds a new object in the lineCollection if product does not exist in lineCollection, but at 24:25 it shows duplicating orders? Did i misunderstood how it works?

http://ift.tt/1HrxeRe