
Then I noticed in the chat that I had successfully captured the pet, even though the battle never ended and the wild pet that I originally clicked on is still running about. The pet is in my journal.

Checking Blizzard forum, certain AOE spell from player on PVP server will break opposing faction's pet battle but there was nothing about ninja-keeping the pet without actually completing the battle. So how did I get to keep the pet before the battle ended? A bug?