It's just as logical to think that the Wii U version will come earlier.
Realistically, it'll probably be a simultaneous release. That's a lot more common, nowadays, than it was 10 years ago. But they never officially confirmed a release month for either version, so what was likely the internal information about release was accidentally used on the website.
People who refer to the Twilight Princess case forget that Twilight Princess had only been delayed from late 2005 to 2006. Zelda U was originally listed as 2015, and was delayed multiple times. They're not going to want to piss people off by delaying the Wii U version further, after specifically focusing on the Wii U version at E3 (they've specifically said they're showing the Wii U version at E3, that NX wasn't going to be shown at E3).