Act III, Scene II: How does Don John's choice of language make the impact of his revelation about Hero all the more devastating to Claudio?

Don John's language is condemning. He leaves no room for doubt and offers to prove his accusations. Thus, he is able to manipulate the other players and deceive their perception.

I came hither to tell you; and, circumstances shortened, for
she has been too long a-talking of, the lady is disloyal. Line 80