From the article:

"The salary advantage for product managers has only grown, says Hired’s data scientist Jessica Kirkpatrick. 'We see that software engineers have always been paid less than product managers, but that the pay gap has widened over the past year,' she wrote by email. The trend holds after accounting for experience. Software engineers, on average, are paid about 10% less than product managers in their first year as well as after six or more years of experience."

So it's not just a matter of PMs being more experienced.