this is correct "a single box" here emphasizes that they got a lot of dishes (two hundred pounds worth) into just one box - not two or three, but one. But that box was larger than normal, because the box was as large as a doghouse. So the point is these people were very bad at packing, because everyone knows you want to pack dishes in smaller boxes so they aren't so heavy to carry, and aren't as likely to break due to jostling during travel.
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