The percentages you listed are not equally weighted; they're weighted by what average consumers spend. People spend vastly more per month on housing and food than they do on gasoline.

So the conclusion that gasoline was the biggest factor in the overall reduction is not true.

Here's where you can dig out the weightings used from the BLS [1]

[1] https://www.bls.gov/cpi/tables/relative-importance/weight-up...