How did Xykon find Serini's diary exactly?

[Good Coyote]

Yeah this is a pretty low-level universe. It's completely possible that, at the time, the Order of the Scribble were some of the most powerful adventurers on the planet. It should be pretty easy to find out pretty much everything about them just from normal research.

I mean the OotS is less powerful than them, and yet pretty much every major area of the plant knows of their existence and has tales of their adventures.

I would agree, except that the Sapphire Guard went around purging all mention of the main quest that they'd been on for the entire time that their party existed.