They have been living in that house for several years. The Zwicks were aware that their home featured a fallout shelter when they bought it in 1999. They didn't actually venture into the shelter until 2010. Over the years the metal hatch had stuck, so they had to crack it. Using the ladder they reached a bunker which has suffered severe flood damage. However they discovered well kept and preserved requisites from the past!
Most fallout shelters weren’t intended to protect a family from a blast, but to keep them safe when the area would be full of radiation and nuclear fallout.
Unexpectedly this family discovered a treasure from the past. Between the findings there were food, clothing, medical supplies, tools, flashlights, batteries. It is rather creepy to live in an era where one day you would be in your living room and the next might be in an underground shelter anguishing about the future.
Sources: Viralnova, Daily Mail