This is an example of litotes. This refers to a figure of speech that emphasizes a point by stating a negative to further affirm the positive. Litotes also tend to incorporate double negatives for effect. The way in which we can tell this is an ironic statement depends both on context and intonation. In this case, the author tells us that the sword was "not useless" in order to convey that it was actually extremely important.
Then D. is explaining how to cure a bee sting and there was nothing in the paragraph that said something about bee stings just for one sentence that said that people don't like bees because they sting
These lines taken from "The Snow Man" might be interpreted in these ways. One possibility is to have an objective view of the nature of a winter landscape without attributing any personal emotions to it. The other interpretarion is the assiciation of winter with misery, sadness and loneliness, the feelings that are related to the picture of the wind blowing with just a few leaves.
