Maybe they intended on having Zelda U release in 2016, and then Zelda UNX in 2017, and Zelda U got delayed because of more work needing to be done. Or maybe they just hadn't made the final decision on whether an NX release would happen, at that time.
For that matter, maybe NX was going to be releasing in the holiday 2017 period, and they brought it forward, thus justifying moving Wii U titles to NX.
Whether it was a stupid contest or not, the contest was "will it release in 2016 or 2017", and people voted accordingly. Those who said 2017, whatever their reasoning, got it right, and those who said 2016 got it wrong. To argue otherwise is to "move the goalposts" and declare a win. Almost everyone who argued for 2016 used the argument of "there's no way that Nintendo is missing the 2016 holiday season". Those who said 2017 were arguing that its first holiday season would be 2017. Whether they predicted a holiday 2017 release or not is moot, because that wasn't the bet in the thread in question.
Maybe. Maybe not.