Poor quality refers to the lifestyle descriptions on page 158 of the D&D 5e Player's Handbook. The food is not spoiled or poisonous, so the food in the warehouse is not dangerous, only of low quality.
A poor lifestyle means living without the comforts available in a stable community. Simple food and accommodation, threadbare clothing and unpredictable conditions result in a sufficient, albeit probably unpleasant, experience.
The descriptions of miserable and miserable lifestyle refer to illness, so it might be reasonable to introduce mechanisms of illness if the food was described as miserable or miserable quality rather than poor.
The complete list of lifestyle quality levels, in ascending order, is miserable, miserable, poor, modest, comfortable, wealthy, and aristocratic. Whenever you see "quality [of thing]" for one of them, you're probably referring to these levels of lifestyle, and the full descriptions will give you an idea of what exactly that means.