So this has been happening over and over, that after clicking "see results" I get a notification, that I tied with my challenger. ALL THE TIME I was flabberghast, because I couldn't imagine, that on the last move, when using 2 healers and a healing scroll, the lowly opponent with just a handful of HP left would have critted my (almost) full HP pet. Since I never pay real attention to the last move, I couldn't vouch for this to definitely not have happened though highly improbable. My pet definitely had lost all HP each time, so I needed to reheal.
So right now I was fighting General Error with my T12. This time I KNOW what happened on the last move. We both froze each other, GE was dead while my pet had almost full HP. I DID NOT see the results page, because like very often I got "This battle does not exist". However, I started the next level and the pet I had fought with before inexplicably was unavailable - because had no HP.
So this time I can be 100 % sure, something went wrong, and I am conviced those other BQs always glitched as well.
edit: "You tied with Meatslab the Resting"
Winner You beat level 17 and are ready to move on to the next level! As a bonus you've been given a weapon. Handheld Hydrus Claws
It just happened again. And it occurred to me, that I wouldn't have finished that level with a tie, right?