The price of regular gasoline in 1964 was actually $0.30. That is the same number the economist used for 1950. What's so hard to understand about that.
The price of regular gasoline in 1980 was $1.19. That's not the same as $0.30.
These prices are listed in the link I provided.
The real question is why the economist chose 1950 instead of 1964 where the price was actually $0.30. My answer would be his inflation calculation works out much more favorably for him to weave his tale by going back to 1950 instead of 1964.
Here's a couple questions for you, do all commodities have the same inflation rate? Why not?
Curiosity causes me to ask, how was that .30 price derived? Was that the "prevailing rate", do you know what kind of formula they use to come up with that price? As I recall in that time period there was a phenomena that was occurring on a very regular basis called "gas wars" was this factored in? Any consumer who was at all savvy in those times watched for them. I know that my parents did and I also know that they seldom payed the going rate for gas because of it. I can remember on several occasions in the 60's that we payed .03 cents a gallon. This was obviously before so many states outlawed selling below cost. We no longer have the benifit of these "gas wars" because of the state laws.