The couplet of Du Fu's "Sunset" is "The wind and the moon are bright at night, and the mountains and rivers are not hometown." What technology was used?

"The wind and the moon rise at night, and Jiangshan is not the hometown." Autumn night, the evening breeze is cool, the bright moon is in the sky, and the mountains and rivers in western Qin are picturesque in the moonlight, but they are not the scenery of their hometown! A faint sentence has a sense of sadness. Du Fu used awkward sentences in this couplet. The word "Zi" should be flat, but it is voiced, and the word "Fei" should be flat. Zi and Fei are the key words in the sentence. Once rescued, they seem to be full of waves. It was because they obeyed the needs of the content that they expressed their yearning for their hometown deeply and euphemistically. Although the mountains and rivers are beautiful, they are not home. This "self" and "non" implies a kind of helpless emotion and a strong homesickness.