You were on when that happen. But you were too busy auctioning your creeper eggs. And you were also using /vanish making u look fake.
I tried this and it works. All you have to do is spam the fishing rod into water, and eventually The_Kraken will come to attack you. In prison The_Kraken can spawn, but you won't be able to see it. If you are in Free-world you will see it named The_Kraken when you spam the fishing rod. Note: You will lose your fishing rod after The_Kraken comes.
The kraken is put in place to kill people who auto fish. Some servers have his dmg so high he one shots people in god armor.
Auto fishing is when you keep casting the fishing rod as fast as you can without waiting for a fish to bite.
Auto fishing is actually a mod included in some hacked clients that does all the fishing for you. It detects when a fish is on your line, pulls the line back catching it and then automatically throws back the line. This is repeated. Things like clear lag interfere with this when it clears entities including the fishing line. Clients with auto fish that just throw out the line continuously are just not made correctly because when it works it should just be like you're normally fishing but without having to click to pull in/ cast out the line. The "Kraken" is included in with the fishing McMMO skill. It spawns in "The Kraken" which steals your fishing rod, pulls you in to the water and proceeds to hit you until you leave the water where it then dissapears. Hope this helped clear some things up
This, I think it was implemented to help stop the use of auto fish, casting and reeling in a fishing rod too quickly in a short amount of time is what I think causes it to spawn.