It was an attack. What you've linked shows the number of transactions that went through (on a particular day). The attacker was creating a lot of transactions in the 1-10 satoshis per byte range. This filled up the mempool.
Ok. My reasoning had a fault. I didn't realize, that the info which I linked only showed those transactions, that went trough.
Is there any chart showing total number of new transctions (both confirmed and unconfirmed) per day?