Just to check was it a level 70 warlock you tried on?
Ive done it myself 
Its probably because its incomplete and ends suddenly.
You beat the dreadlord, the lightforged walks off and kneels down, and thats it. No more quests
They say the warlock customisation will be in a later ptr update so im assuming the rest of the questline will be too.
He is a lightforged
I typed out that quote a few hours after the ptr came out (linking to verify the screenshot)
The explanation isnt the best considering that all the destruction and ruin his people have faced is due to the exact thing he now learning.
But hey, its what theyve gone with