What does Shu dog mean by barking at the sun?

A Sichuan dog barks at the sun (because it is rare in foggy areas)-an ignorant man makes a fuss about things that are strange to him.

Shǔ· Pei Kun Fei Li

[Explanation] Shu: the abbreviation of Sichuan Province; Bark: A dog barks. It's rainy in Sichuan, and dogs don't often see the sun. When the sun comes out, they bark. Metaphor is rare and strange.

[Source] Liu Tang Zongyuan's Answer to Wei Zhongli's Book on Teacher's Way: "Qu Zifu said,' Dogs bark in the city, and it's strange. "The servant went to the south of Wenyong and Shu, and the rain continued, the days were few, and the dogs barked at sunrise."

In geography of senior high school, when the teacher showed us the distribution map of acid rain in China, the whole Sichuan Basin was dark and the acid rain was so serious. So the teacher told us the story of "Shu dog barking at the sun". At that time, I thought the dogs in Sichuan were really pitiful. In ancient times, they didn't know that the sun was because of the weather. In the new century, they can't keep up with the times because of pollution.

By the way, our classmates all marked the dark area as "Shugou barks at the sun". I felt so kind when I saw this question just now.