Bunny Soul can be the reward from any of the Shadowlands pet battle world quests, not just in Ardenweald. Got mine in Maldraxxus. Ther're confirming comments for all four regions in Shadowlands on wowhead: https://www.wowhead.com/item=187858/bunny-soul#comments

Hello, thanks for bringing this information up.
I'm currently abroad and cannot fix this right now, but I'll pick that up asap when I'm back.