Now user putl3 was removed...
I think it was a bot, i.e., a program script. As pcuser clearly explained it's humanly almost impossible to attain such a high score and number of puzzles played. I believe it has a mechanism to submit repeatedly the same grid-posting to the game server to each puzzle under a legit user. This explains the low completion percentage (about 65 %). Anyway it played some 12,000 puzzles in less than a week before it was removed from the server (for good).