The point Verizon is making here is that Netflix has not done due diligence to verify that the specific customer they are showing the "Verizon Sucks!" message to is having connection issues that are provably Verizon's fault.

It seems to me that they're stopping one foot shy of calling Netflix out for libel. It's not libel if it's true, so it might be better for Netflix to only show the message when they can prove that the specific connection is being slowed because of the interconnect (or lack thereof).