Yes, I understand that. But if they state that the power requirements are 5V@4A, then that means the device can reach 4A of current consumption.
Now, USB-C PD 3.0 and PD 3.1 can reach that, but I doubt that this router has USB-C PD. But that is ok, as long as they provide the proper power adapter and a cable that supports 20W then it is all good.