It's a bit of a strange article. It's kind a obvious that in the case where prices of different goods/services increase by different amounts, there is not a sin

It's a bit of a strange article. It's kind a obvious that in the case where prices of different goods/services increase by different amounts, there is not a single metric that would reflect the price increase. Also it is clear if we're trying to make some kind of weighted mean, the weights will differ for different groups of people, reflecting different consuptions. So depending on what we want to measure we'd chose different weights. If say for low income population interest rates play a bigger role (i.e. due credit card debt), than that may have significant weight.