While a great story indeed, I am going to be forced to say IMHO that is exactly all it is. A great story. I am 55 years old and had all kinds of great and terrible things happen to me in the course of my high school. I clearly remember everything from the 1st time I actually smoked pot to the 1st time I go pulled over by the police, while having an ounce of weed in my car under the seat. Now ask me if it was a Saturday or a Thursday that it happened. Heck I do not remember what day it was, and find it hard to believe that someone who themselves said it was no big deal, just another of his typical things that he did, would remember 37 years later that it was October 3rd at exactly 420 pm. Now I can remember my most memorable birthday party as a child, it was June 29 only because that is my birthday, every year. What time was the party? Assuming it was daytime but heck I don't remember. For me there are just way to many holes in the story to be taken as fact.
I will say it was an interesting read though, just not sure if I personally would say it was factual but you are all welcome to believe it if you like. It did have to start somewhere and someone did have to coin the phrase. Maybe I am all wrong and people are able to remember 37 years ago what they were doing on October 3rd 1970. I know I can't.