The WiiU checks often for a new update. So maybe your error is only that, a failed checking.
You should rather be alarmed if it DOESN'T appear. Keep that in mind if you're planning on removing the DNS to use eShop once in a while! Always a good idea to look for the download error icon.
https://wii.marcan.st/wiimpersonator/runlog.wiiu.USA.txt
Wiimpersonator is probably the easiest way to tell if there's ever a Wii (unlikely since it became a dead platform in what, 2012?)/Wii U update.