But you can't have a meaningful discussion about it if you do not list the weight of the price hike in your expense pattern.
When gas for your car normally takes up 10% of your income, and this price doubles, your personal inflation is 10%, not 100% (assuming no other price hikes).
Perhaps he is only spending 10% of his income, but it doesn't really matter for what he is talking about.
https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=pet&s=e...
I would say that you can't just look at average prices for the US. Look at the California version of that chart [1].
July 2021 to July 2022 is an increase of about 38%.
If you look at June to June it is 50%.
While not double, it is quite a bit more than 30%. Depending on the area the person quite possibly did recently experience double the price like I did.
[1] https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=E...
Typically statements like "this increased 100-150%" are used to support the theory. The only thing I'm saying is that individual price hikes are meaningless without any information about the total expense breakdown.
That said, I do agree that CPI is typically slightly optimistic.
In general when the facts are not recognized ie. pretended that they are not happening, long term it is bad for the country as a whole.