"[Greydath] is able to read the classes of others."
No, he isn't?
From Interlude - The Isles of Goblin and Minos:
“—I came to tell you that the Redfangs of the High Passes are gone. Their Chieftain was Level 38, I think. Two classes. Garen Redfang."
The "I think" there implies it was a guess, so unless there's something I've missed, there's no reason to assume Greydath is able to "read the classes of others".