Shouldn't have anything to do with meeting Wuldon. The quest can be pretty buggy if you don't solve it your first time through. If you remove all of the weeds, leave and reenter, then remove all the weeds again, you will have just made it impossible to inform Uffe of your success. Same thing if you try for a second amulet.
To be able to complete the quest, the game only makes two checks - one that you have the Moonstone amulet in your inventory and a second check on your quest status. Wuldon has nothing to do with either, so it's unlikely he was the culprit. The quest status, though, is likely the issue. Remember how above I mentioned that doing certain tasks twice can make the quest impossible? Both of those alter your quest status by incrementing its value. However, this isn't reset when you exit the cave and you can repeat the action as many times as you want, further incrementing your quest status. Uffe only checks for a specific value, not a value greater than a specific threshold, making it easy to accidentally break.