I agree that's a lot, but we need to bear in mind that active can have a lot of definitions. From the article:
"active in this sense means the number of accounts that were modified over a three-month period, including changes of avatar, subscribing to a new follower or tweeting"
Three months is a long time for activity - monthly / weekly / daily active user metrics are more common. Also, it (apparently) isn't counting a visit as activity, just these actions. That just makes this a weird metric to benchmark against.
"active in this sense means the number of accounts that were modified over a three-month period, including changes of avatar, subscribing to a new follower or tweeting"
Three months is a long time for activity - monthly / weekly / daily active user metrics are more common. Also, it (apparently) isn't counting a visit as activity, just these actions. That just makes this a weird metric to benchmark against.