So that NGINX config portion looks like it would match both the apex domain and the www domain, and you’re instruction it to handle all paths and send it to your home page, which I assume is in /var/www/EXAMPLE.com/html.
You have to keep in mind that NGINX config is loaded at run time by concatenating all the config files it finds, including the ones in sites-enabled. So you might have a conflict somewhere that causes the www to redirect to your forum. For example, you may have another portion of NGINX config that comes first at run time which catches www.EXAMPLE.com and redirects it to a URL that matches a server block that proxies to the Discourse server. In fact, that’s the scenario I think is happening. Posting your complete NGINX config will help determine whether this is happening. On the running server, you can use the nginx -T command to dump the complete NGINX config currently loaded to stdout.