[Dove]

It means you were able to fake the algorithm out. Consider a very simple algorithm that guesses based on your previous two characters:

  df  d
  dd  d
  fd  f
  ff  f

This is presumably much simpler than what the page is doing, but will nonetheless work pretty well on humans by looking for alternations and long runs.

This algorithm is trivially defeated (chance of guessing 0) by the string

ffddffddffdd

Since that holds a pattern just long enough to get the algorithm to guess based on it and then switches.

For a little while, either intentionally or not, you must have been doing a more sophisticated version of this.

With perfect knowledge, it should be possible to get it down to 0.