Thanks to everyone who tried to help out. I finally had time to search through the forum some, and apparently it happens a lot. Several people have posted about the same thing.
But most of them said it was only about 1-2 tablespoons worth of oil, and that once they dried it out, they drove around a bit without the drive shaft, and it never even got wet again.
So, I dropped the shaft, dried it out, swapped the rear cv joint, then rechecked, and it was still dry.
Uss2defiant, some others had said the same thing you did.