A nice, concise explanation from NC :

Let’s skip the indefinite period up to the IXth century. After this, begins a new chapter in the history of China allegedly from 860 to the year 960 AD. That is approximately 100 years of darkness. L.N. Gumilev calls it “the dark age” and builds some geophysical theory that should explain the absence of records. The steppe dried up, and dusty hurricanes hit the unfortunate country. However, in our opinion, it is not in the tornadoes, but in the incorrect dating that hit.
L.N. Gumilev continues: “The great silence of the desert was widening, engulfed steppe and covered it with sand streams. That is why the chroniclers of the 10th century are silent about the events in the center of the continent. For A Long Time No Events Happened There “[212], p.152 This is the last blind spot in the history of China. The subsequent epochs are allegedly well documented [212], p.176.
    As we have already seen, the “dark ages” of Scaliger’s history are usually artificial junctions between neighboring chronicles, caused by their incorrect position on the time axis. In this case, chronologically, the last “dark ages,” as a rule, mean the era of the beginning of a real written story, yet very poorly illuminated by the surviving documents. We have already repeatedly faced this in the analysis of the history of Europe. See books “Foundations of History,” “Methods” and “New Chronology of Russia.” 
Therefore, we object to L.N. Gumilev: the events did happen. However, perhaps at another time and in a completely different place. Consider here those few legends, which came to us from the darkness of the Chinese history of allegedly IX-XI centuries AD.
    Firstly, this is the legend of the conquest of China by the Cidan. This story, due to the imposition of the Cidans on the Macedonians = Ma-Cidans, naturally, one wants to compare with the legend of Alexander’s Macedonian conquests.
    Secondly, this is the legend of the Son of Heaven. The latter copies the narrative about Jesus Christ, mistakenly dated by the XIth century AD instead of the original XIIth century.