Although you are right, it could be a spammer, there is another possibility that I wanted to make sure you knew about:

There is a chance that it's someone who is infected with an email virus and isn't deliberately trying to do anything bad. One of the characteristics of certain recent email viruses is to spoof the return address using a random name from the sender's address book (instead of using the sender's return address as older viruses did). I think they do this to make it more difficult to quickly identify and quarantine the infected machine.