Flowing clouds mean: describing articles is natural and unconstrained, just like floating clouds. Describe the natural fluency of poetry, calligraphy, painting and thinking; Describe things that flow and disappear easily; It's fast and light.
Writing like a cloud means: describing the chic movements when waving, such as flowing clouds pouring on paper.
From: Tang Du Fu's Song of Drinking Eight Immortals: "Zhang Xu has three cups of grass, took off his hat and exposed himself to the top of the maharaja, waving paper like a cloud." It means that Zhang Xu drank three glasses of wine and wrote a book with a wave of his hand. At that time, his name was Cao Sheng. He often takes off his hat in front of princes and nobles and scribbles books. If God helps him, his book will be like a cloud of smoke on the paper.
Flowing like water, flowing like smoke:
Flowing clouds and flowing water, writing like clouds and smoke: metaphor poetry is pure and natural, unrestrained or insignificant.
From Su Shi's Book of Pushing Officials with Xie in the Song Dynasty: "Books, poems, and poems are familiar, like flowing clouds, with no definite quality at first, but often do what they should do and often stop at what they should do."