Regardless of how its phrased, you want your Router to respond to the pings from the PacBell Diagnotic equiptment.
Normally, when someone (like a hacker) pings your IP address, you want your Router to give no response - like there's nothing there.
But when your Service Provider is trying to test your equiptment you want your Router to respond fully to each ping from the WAN.
The WAN is the segment from your Router to the internet, while the LAN is the segment from your Router to your computers.