When Google updates, it can take a while for it to reach all the servers. If you have a VPN, try switching browsers and VPN servers.
It’s possible to have a good amount of say in what Google does, but they can still override everything if they want.
When I search again (possibly with different cookies), they are A/B testing a completely different interface. It depends on what server you hit and whatever they are up to. 
Edit: I tested again in a private Safari window (the others were Firefox), and the Discourse site moved up from #2 to #1 with the table view. I also tested again with a clean Firefox container tab (no cookies) and different VPN location and see it at #1 there too. There isn’t complete control over Google there, but it’s looking much better so far due to the changes to the title and meta description. I’d make a note of the time you changed it and you can see if it affects click-through rates in Google Search Console and traffic in Google Analytics. It might take a few days to settle.
Edit 2:
It’s because the plugin that you’re using only changes the SPA frontend of Discourse, but the bots still see the same bot-view that looks like this:
If you want to see what Google sees, install this extension in Firefox and set the user-agent to Googlebot. (Be sure to set the user-agent back to normal afterwards, otherwise you’ll get blocked by many websites.)
I think it’s better that way though, because when you get the table-row view in Google, it looks like your site is really active, sometimes with 100+ replies and thousands of views on topics.