Apparently this was a school project, with a team of 4, made in 10 days...and it was their first time coding in DirectX.
So in reality it was likely 1 person coding while the other 3 jerked off. It was made in 10 days, but technically it was more like a month in work hours because the 1 guy doing the work got maybe an hour of sleep per day.
I love how at 0:52 when the player whips the rocket launcher around to the left the rockets launch sideways. That must have been planned or I know nothing about how games work.