A possible way to resolve this contradiction is by taking cost reducing technologies into consideration.
Perhaps (example with made up numbers follows) in 1960 a gallon of milk cost \$1 to produce, package and market. Due to strong competition, the consumer could get this for \$1.02, meaning a markup of only 2%. Today, due to technological advancements, the same gallon of milk's production, packaging and marketing cost could be lower, say \$0.80. However perhaps there is much less competition, and the markup is now 30%. This would make the consumer price of this gallon of milk \$1.04. The price jump from \$1.02 to \$1.04 seems negligible, something most people would call low inflation. (Especially if this took 60 years.)