So Mooby isn't a fundamentalist who thinks the Bible is infallible. So? That doesn't make him an atheist or a Poe. "Christianity" has always been a plural phenomenon, with the exception of a few brief periods of putative unity imposed during the late Roman Empire. Even then, "the Church" had to have several Councils where compromise doctrines were hammered out and "heretics" excluded. Some groups like the Nestorians and Coptics were never really homogenized into the fold, and Gnostic-flavored versions kept cropping up (e.g. the Cathars). Nowadays, "Christianity" ranges from Fred Phelps to Bishop Shelby Spong. Mooby sounds to me like he's closer to the Spong-ish end of the spectrum.
Why should atheists argue that the "Bible-believing"[1] Protestant fundamentalists are the only "real" Christians? Better, I think, to acknowledge that Mooby's claim to be a Christian (assuming he makes such a claim) is just as good as the Pope's or Pat Robertson's anyone else's. The fact that Christians themselves can't ever come to agreement on what "Christianity" is, except at sword-point (and only temporarily even then) is, IMO, a pretty good argument against Christianity. At least it shows that they can't ever validate any of their ideas about "God," the "spiritual realm," the Bible, etc.--a point with which Mooby might well agree.
Highest possible level of Christianity:
Believe and obey
everything in the Bible word for word. Where there are contradictory rules, you must choose one or the other. I have never heard of this type of Christian actually existing.
Where I draw the line for the lowest possible level of Christianity:
Believe Jesus died for your sins. Believe you will be with him and the other invitees in Heaven for eternity. While you're here, do whatever the fuck you want. Jesus gotcha covered.

I had to look up Spong. Saying Spong is a Christian is a semantic issue. You can call Spong a Christian if you call Einstein a Jew.
If I believed that Mooby believed everything he's posted that he believes, I would definitely consider him a Christian. In real life, I seriously doubt that he is Christian.
But, if you were the creator of the universe, wouldn't you make it extremely clear to the reader of "Your Word" that Moses went rogue on your ass?
If I were the creator of the universe, and were writing a book, I'd probably follow Moses' speech with, "And then Mooby shoved his foot up Moses' ass for saying that." Then I would entertain myself seeing if people took that literally 3000 years later.
If you define "POE" as "a person whose Christianity or non-Christianity cannot be determined because the content of his/her posts, though extremely ridiculous, could have been made by an actual Christian", then I wouldn't call him a "POE", because I am as certain as I can be that Mooby is not a Christian. It's everything gathered together: his posts, his amount of time invested here at WWGHA, his high intelligence
[2], etc.