Everyone has seen it, and everyone overreacted. I doubt anything he said is false. The things people are most upset about were things he clearly states are just his opinion.
In terms of Warners being worried, it was just in regards to the Post-Trailer 3 reaction. And no reasonable fan can say the reaction after that trailer wasn't worrying.
However, the trailer yesterday saw a huge shift in sentiment. People who were turned off after trailer 3 got back on board, and some who were never on board to begin with got excited for this film.
At worst, McWeeny's info was just immediately outdated (as WB probably isn't worried anymoe after yesterday's trailer reaction).
And in addition to that, McWeeny said that Affleck was good, and Eisenberg (the factor everyone was worried about, and was the main point of worry) is great. And a few months ago, Collider Frosty (also reliable) said WW is the real star of the movie.
So just calm down. There's nothing to worry about.
After yesterday's trailer and McWeeny's comments on Eisneberg, I've never been more confident in BvS.