Lv99 Liberator giving Requiscat

I seem to obtain the WS Requiscat when equipping the Lv99 Liberator weapon with Afterglow. I can even use it in battle which makes for a pretty hilarious looking animation (Swinging the scythe around like a sword and all).

There seems to be no specific requirements of having this happen, however I've yet to unlock any of the merit WSs in any form. I also have completed the quest in the past to be able to use Insurgency anywhere as well, if that makes a difference. Just equip the weapon, and it's in the list in any zone under any circumstance.