Random new mastery pages appeared and disappeared on my league account.

I have 6 mastery pages currently, and suddenly while I was queuing up for a new game I noticed that there was suddenly about 17 pages! These were named things like "The Blade" and "The Lover" and "The artist" and "KNOWLEDGE". This was really confusing as they left shortly afterwards. Is this a teaser for upcoming content? Is this a bug? Is my account compromised? I can post links to a few screenshots I took after a chunk of them disappeared.