After the first time watching this I was sure it was staged, like he hit the door with his arm to create the noise. However, after watching it again and again, he clearly knocked himself out by accident by running into it lol!
Apparently the guy was looking for something in his truck when he realized the item was actually in the house. As he took off running for inside his wife closed the door assuming they were ready to go. That's when the husband got knocked out for the count!