I am not a Wix user but I just came noticed they are using WordPress plugins like Yoast SEO and other plugins on their official blog post’s http://www.wix.com/blog/2016/04/why-online-bookings-help-you-sleep-better-at-night/ source code. But I am not 100% sure as it seems like they are trying to hide WordPress. I also checked with popular chrome extension web technology detector Wappalyzer and it shows Wix but not WordPress. Anyway they devised a brilliant way to use WordPress and goes undetected, this is very surprising for me as I assumed has their own blogging system.
Below are some screenshots I gathered: