I was like 156 on my wiz and randomly decided to kill wt for shits and giggles and it spit a skill necky into my bag. So I firmly dont know how it works tbh.
Just because you got the achievement doesn't mean you completed the quest which gives the skill necklace reward.
The quest is for new low level players and swaps out for the famer quests once you are too high level.
Woomataurus drops skill necklaces naturally anyway
I read this before and started going through the quests on a new character at a low level to get it. However I clicked on one of the halloween NPCs just to talk to them and they gave me so much XP it shot me from level 30 to level 58 and cancelled out my ability to do the questline anymore. I mean cool for quick leveling, but I was really trying to get that skill necky.