It makes it less surprising to me. Back in 2006 I believed Hersh when he reported that the U.S. had troops inside Iran laying the groundwork for an imminent American attack. This was also based on anonymous sources. After the attack failed to materialize, I learned to take such reporting with a large grain of salt.
He used to be credible. Then unfortunately a lot of shady people learned they could manipulate him and get away with it, and so they've done. He can publish something like this and when anyone says, "prove it" he can't. Because Top Secret.
This is something that will always be problematic when reporting on something that hasn't happened yet. As the future hasn't been written, there's always room for all actors to adapt and change their plans.