Possibly semantics but I think there is a subtle difference between the 2. I assume he will have judged the info he was given at the time in good faith, formed an opinion one way or another and posted what he did to share with GOTers. That is the information that could have been "misjudged" as you have stated. There is then the scenario that follows where regardless of the judgement made of the original information, the situation simply changes. That change of situation will undermine any judgement that is made regardless of whether you got it wrong or right based on the original info
If we did sign Mata and Witsel today or at any stage in the remaining window it does not necessarily mean his information was "wrong" it could just equally mean that once again the situation changed. Some will no doubt point that they feel it is an indicator that there was significantly more to the original release of information and see it as some sort of vindication of the person releasing it.
If we fail to sign either of them by the time the window closes, that too does not necessarily mean the information he was passing on was wrong, once again it could simply mean the situation changed.
Unless the club come out and make a categoric statement that at no stage did we make a move or have any agreements in place for these 2 players then we will never know, and that is unlikely as it tends not to be common practice (I think).
These are complex affairs, not everything is black/white or right/wrong - things change, situations are fluid etc.......