User blog comment:Miskos3/Fairy Tail Chapter 488: The Two of Us, Always, Review/@comment-104.56.248.166-20160608000806/@comment-7418318-20160608064851

That aside, when would he have had a chance to tell anyone?

When he "came back" to the guild he was unconscious. Then he woke when Jacob was already attacking and moved off to attend the negotiation right after.

There's also a good chance that he doesn't even believe Zeref in the first place. Sure shooting the book might be quite convincing to some people, but does it really proof anything? It could (from a character's perspective of course, since we know it's true) just as well be a cursed item or a spell that works a bit similar to Kain's Mr. Cursey, but forcing wounds on the victim rather than movement.