Sure. But you need to clearly define this. Is looking at Facebook really that different from a EC payment? Both are just instructing some electronic device to send packets over the internet. Having a call via VoIP can be abstracted to the same thing.
I agree that the sledgehammer approach of saying 'everyone does' is not helpful, but neither is an unclear and inconsistent definition of use.
An actual solution might be to ask who directly pays for internet access or who knowingly uses it; the latter of which is probably what the study found.