SPAMers will often say that they are in one country when they are actually in another country.
SPAM is typically sent via a botnet made up of computers all over the internet, so the SPAM could pretty much be coming from any countery in the world. The person sending the SPAM could be in any country.
The ISP could be using a network of email relay servers. The email client could submit the message to one server locally and then it get rerouted through the ISP network and go out a different server entirely. You would need to look through the entire header to trace the message path. Just looking at the last IP address does not give you the whole story.