It's making the comparison to illustrate that the OS/User has no way to differentiate between a trusted router doing the blocking and the ISP blocking certain d

It's making the comparison to illustrate that the OS/User has no way to differentiate between a trusted router doing the blocking and the ISP blocking certain domains/injecting ads. If you want to block domains on your devices, doing it on your devices themselves will be more reliable and implicitly requires you actually own & have admin rights on the devices you want to block domains on.