There are times when a speaker makes a positive statement about a person and intends it as such, but negative and harmful information can be inferred from his words. The Torah would not consider one who does this to be a holech rachil, peddler of gossip, since both his intent and his words are clearly sincere and positive.
Rabbinically, however, this too is prohibited, under a category referred to as avak loshon hora, the “dust” of loshon hora, which is spread by way of carelessness.
A common form of avak loshon hora is where one sincerely praises another person, but in doing so, alludes to a shortcoming of that individual.
“Who would have believed that he would have come this far?” clearly suggests something negative about the person. Such a statement can cause the person embarrassment when said in his presence, and can be harmful to him even when he is not present. Hence, it is forbidden.
