Exactly. A Christian is also an atheist. They're Odin atheists. Or Vishnu atheists.
The terminology is just wildly out of date.
For some theists, the gods of other religions are incomplete images of God. And this has been
Lion IRC's argument, presented several times.
In the protestant sect I attended, the other gods were demons leading humanity astray.
So trying to find the common ground and saying "see, you're like me to this extent at least" is a strategy that can blow up in one's face. If there are theists who disbelieve the other gods, it's not likely for being skeptics, it's not likely for thinking the concept is flawed or the evidence is lacking.
They don't lack belief in gods or disbelieve gods, because they believe in one, so no theist is an atheist.
What, then, is a Christian in regards to Odin? I don't know. I think I'd ask the theist, rather than announce at him what he does and doesn't believe the way they tend to do with atheists.