That headline is… incredibly inaccurate. They’ve pledged to each other to avoid porn, and have software that throws an alarm (visible to each other) if they view it.
“Monitor Each Other’s Porn Intake” implies that they are seeking out porn and sharing it with each other, which is not what is happening here.
I think there are plenty of legitimate concerns here, but father and son sharing porn links is not one of them.
Also, I imagine young Mr. Johnson has at least 1 Android tablet or other burner device that is unknown to Dad.