Sounds like there's some sort of Uber cult which uses lead Magikarp as part of their rituals. Maybe there's more here than meets the eye with this little fish?
I think this was probably some April Fools joke played by the #ubers gang. They went on the ladder en masse with Magikarp leads and quit, and in a day managed to rig the stats.
Or there was a glitch/hack. Either way, this is wayyy too much work for a sane person to do in a legit manner.