I cannot remember, are the Fomor signatories of the accords? If they are, the rest of the signatories could have been surprised because they thought the accords would protect them as far as leading to conversation before battle. I find it hard to believe that the Fomor could have killed Gwynn ap Nudd without someone knowing about it. He was evidently alive to arrange and lay down some of the protections on the Peace Talks meaning he was in contact with the other accorded nations. They took him out after the protections were laid, but before their appearance so that they could bring his head to the Peace Talks. Killing a head of an accorded nation, that should have been caught right away in my opinion.
