This refers to one of the most famous philosophical puzzles in Chinese thought. Zhuangzi, a 4th-century BCE Taoist philosopher, told of dreaming he was a butterfly fluttering freely among flowers. When he woke up, he couldn't tell if he was Zhuangzi who had dreamed of being a butterfly, or a butterfly now dreaming of being Zhuangzi.
This story became a cornerstone of Taoist philosophy about the nature of reality and identity. For Zhuangzi, the boundary between dream and waking, self and other, was fluid. The tale suggests that what we think is "real" might just be another kind of dream, and that transformation is the only constant in life.