Forpli is right, and there is nothing wrong with their screenshot.
You can see this in my shared screenshot as well (this was taken a week after Zorin 18 beta release):
Back that time I also had tried looking for ways to check where is the Beta tag mentioned but found none. It was always displayed as Zorin OS 18 Core even on beta.
The only way was for me to keep a track of the updates and by noticing the Packages related to Zorin system. And then Zorin 18 release blogs mentioned that Beta users only need to apply the latest updates to get the stable so if you have performed the latest updates available then as per the Zorin 18 release blog, you should be on the stable version now.