"The Ichigo Infection Incident" was indeed a term that did not exist during Xiang Shan's lifetime.
In Xiang Shan's memories, there was indeed an incident that caused… severe consequences because of genetic weapons.
But that incident… perhaps could be called an "extinction event", as it indeed caused widespread extinction of species, but it was not beyond reversal by human effort.
For Xiang Shan, this was not a point from history books that required special memory. For him, the "Hero War" was an ongoing process, and what later generations called the "Ichigo Infection Incident" was just a part of this continuous process.
Perhaps it had a profound impact on later generations. But at the time, it was just a negligible part of a series of major events.
Moreover, Xiang Shan was very sure that while he was alive (or rather when Martial Ancestor Xiang Shan himself was alive), this was an event that could be reversed by human effort.