Does "quite critical" mean plants or weather?

The weather is quite critical, which means knowing the arrival of autumn from the fall of a leaf. It comes from Huai Nan Zi Shuo Shan Xun: When you see a leaf fall, you know that the year is coming to an end; Seeing a pot of ice, knowing the world is cold: from near to far, later generations refined the idiom "quite critical" to describe the weather change, which was later extended to a rhetorical device to predict the overall trend or result by observing individual phenomena or details.