An iodine test is used to detect starch, which is a polysaccharide. This is created by plants from the monosaccharide that they produce during photosynthesis as a means to store it in their bodies. The starch is used both as a food supply by plants and converted into other organic substances that allow plants to grow.
If an iodine test conducted on a house plant yields negative results, it implies that all there is no starch present. The iodine test cannot detect monosaccharides.
The plant could not have built up a sufficient amount of starch as it may be small or if it were not able to create enough carbohydrates through photosynthesis. This could be due the fact that it is not receiving a sufficient amount of sunlight inside the house or there is a shortage of water. Inside the house, the amount of carbon dioxide required would be sufficient but the other factors could be in short supply. As a result the plant starts breaking down starch to use as food for itself and also does not have enough of the primary organic units that starch is made with.