Yeah, the article is comparing the blackout, which started on a Monday, to the traffic a previous day, a Sunday.
I don't have any deep insight into social media traffic, but 6.6% Day to Day with no other context of what a normal usage pattern might be is worth very little.
The average time on site being the lowest its been in 3 years is more damning, although easily explained by the pattern of "I go to my favorite sub, oh it's set to private, ok going somewhere else", not to mention broken google results.