Has anyone else gotten the "Release the Kraken!" challenge or know anything about it?

I was playing Tunnel Town, at level 37 and had no more challenges left on my list, when all of the sudden there was a notification saying "Challenge Complete! Release the Kracken!" and showed a picture of a Squid Bunny. This happened while I was simply buying carrots, and when I had no challenges left in the list, so I have no idea what I did to "release the kracken," and complete the challenge!

It gave me enough XP to level up - I am not sure whether I also earned gems or stars with the challenge, because I wasn't expecting it so I just clicked the little 'x' and so closed the notification, and I leveled up so I got three stars from thay - but I think I got even more stars,  I can't remember now how many I had before the challenge but I think I got more than just the three from leveling up. Anyways, I am glad for this challenge but I am curious as to the details. Does anyone know what I am talking about or know anything about this challenge? Thanks in advance.