Just looked it up and the first machines that shipped with M1 were released on November 10th so you might be right considering they never said 2 years from WWDC 2020 specifically.
Right, I just reviewed his comments at the end of the presentation, and it's easy to interpret Cook's comments as roughly 2 years from the first Mac at the end of 2020.
https://youtu.be/GEZhD3J89ZE (roughly 1:45:00)