The facts don't come into it that much. The Left considered it a major victory for the Left.
Kind of like the terrorists in Spain who considered the government change there a major victory for their bloody tactics. The fact that there were other equally plausible and unrelated reasons for the election results doesn't change their impression, or change the future attacks that will result.
The fall of Saigon and the resignation of Nixon were the pinnacle of the Left in America. The 1960s crowd went on to enthusiastically absorb the Democratic Party, and you can see where it's led them.