The accepted definition of inflation is a general increase in prices.
The best measure of this is not self-evident, and CPI is an estimate of the cost of a basket of goods that represents basic living expenses. The old CPI series did not account for the quality and durability of the goods in the basket which was increasing over time.
Transportation is a big component of CPI, and it was observed that while newer cars cost more, they also last longer and have more features (airbags, antilock brakes, more reliable engines), which meant that CPI had become a hybrid inflation + technological advancement index.
There are various ways to fix this, but it's no conspiracy.