Yeah, I had this too. The "tribute" treaty offer is apparently you give him 10% of your income. I was confused because he was weaker than me and offered money to get this treaty, and accepted it. Not like it really mattered, since I was overflowing in gold, but it was still kind of odd. Why would you offer gold, to get gold? Makes no sense to me.

Edit: Here's a SS of what we mean:

I was once offered 10 magic knowledge for 10 magic knowledge...

hmm...i was also offered over 900 gold from magnar for the "tribute" treaty, but magnar was on the top of the ranking list and i was second.