We've heard of the mythical "god boxes." In Journey into Nyx, we had actual "god packs," where every card in the pack was a god from the set.
Now we have... fetchland boxes? This video seems to suggest so. In it, the creator opens a full box of packs, and finds a fetchland in every single one of them. I'm not sure if this is a printing error or a special little easter egg from Wizards, but either way it's awesome.
That said, keep in mind this is going to be a very small print run regardless of whether or not it's on purpose. Fetchland prices may have a little more room to fall because more are being opened, but they aren't going to change significantly based on this easter egg/print run error alone, so you don't have to worry about this crashing the prices of your cards.