He is a spy of sorts. He has done much travelling recently and has seen many things, including the PC's battle with Sarevok, and heard about some of the other NPC's travels. He has been doing this because he believes <CHARNAME> can help him with his quest....
And besides, doesn't Yoshimo say something like "You mean you haven't heard of me?" when he meets you? And doesn't he claim to be well known?
This all sounds much cheesier written down than it did when I had the idea in my head....
The story may change: Arcajarn may only have heard of the PC and Yoshimo. He may not have actually seen them. If the latter was the case, it would seem pretty ridiculous, as I stated earlier. I just have to change a few dialogs.

I can't believe I even had that idea in the first place. I must have been tired......