The odd thing is I didn't sign up / join any Beta, it was just a normal app update and there was no option to opt out, I had to uninstall the app then use a backup copy of the apk to reinstall, now my phone and tablets keep offering (auto update is off) me a WU app update which I'm ignoring.
Also can't find any mention of a WU app beta anywhere on Google Play even within the WU app page.
EDIT
Just found out where beta option is and I definitely didn't sign up for that.
Interestingly also found out that the Play app doesn't offer me the update for either of my Nexus 7 tablets (an original and a 2013 version) it warns that the app may not be optimised for my device.