[rob74]

If you look at the failed attempts in the article, you'll see it's not so easy to get 100% correct with 6 guesses. For example:

SLATE, CRONY, HOUND, BOUND, POUND, MOUND (correct: WOUND)

SLATE, SHARE, SHAME, SHAPE, SHAKE, SHADE (correct: SHAVE)

...so sometimes even if it gets 4 of 5 letters right on the second try, it still has too many options left. Of course in cases like this it could go "one step back" and try a word with (most of) the letters that are different between these words (HBPMW or MPKDV). So try different words until the number of options is narrowed down sufficiently.