Answer: in the first passage the author means lonely as the regular definition which is being alone. He talks about the flowers and things because he is having alone time admiring them. He also talks about how he usually go on this walk to admire plants. Also, he talks about how he is so alone that nature is pretty much his friend.
The second passage refers to being lonely as in the greatness in enjoying your imagination when your friends are not around. For example, boredom can be used as the way this passage describes being lonely. In the first stanza, the poet says that he was wandering lonely as a Cloud that floats on high o'er vales and Hills. The phrase refers to him being roaming around without any purpose. He was all alone like a cloud that floats high in the valley.
