You didn't learn it. It was on global preview which ended an hour ago. There was an announcement on the forums and in game, although not at log-in afaik.
[21:51] System Announcement: The preview period for Beckon the Naga, Time of the Red Spiral, Mass Rejuvenation, Frost Scythe and Oath of the Firstborn has ended. If you wish you continue using these spells you will need to visit your Guildleader, with the exception of Beckon the Naga which can only be found on scrolls.
It was on preview so everyone had free access to it. You never actually spent spell slots on it or learned it from the Guildleader.
It is now off preview and you'll need to spend spell slots if you wish to keep it.
-Raesh
"It was wise enough to know itself, and brave enough to BE itself, and wild enough to change itself while somehow staying altogether true." ― The Slow Regard of Silent Things
