Taking some vague numbers from that article, a low-income salary might be $20,000, which gets an increase of 5%, so $1000. Meanwhile a high-income salary of say $100,000 gets an increase of 2.5%, so $2500. Which one is the bigger increase?

Measuring these things in percentages hides the fact that the underlying numbers are immensely different. Perhaps if we reported numbers differently, we would say that the pay increase for the high-paid worker was 2.5x the pay increase for the low-paid worker.