It’s a spoiler for a completely different and unrelated novel. All he really says about New Sun is that despite his claims to remember everything, Severian is an unreliable narrator, that it may be useful to look up the older stories connected with the names of characters (especially if they share names with Catholic saints) and that "things returning to life" is a recurring theme in the book, which is worth paying attention to.

He also says that Wolfe told him who Severian's mother is, but leaves that undisclosed.