Sam's Bunk Bed

Hopefully this gets out before IMDb closes the message boards, but why does Sam Dullard have a bunk bed in his house? Should we assume that the house is a one bedroom and his mom sleeps on the bottom bunk? The episode I am currently watching is about his Dad coming for a visit. The night before he tells his mom that "he has not had any liquids before dinner" because he was getting excited for the visit. He is then seen climbing up the ladder to the top bunk.

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