When I switched over to the wordpress article you linked, I noticed I am logged in and ready to comment. Curious to know what method was used to accomplish that since both sides are connected.
It uses your NodeBB Login, so you could probably get away with not using Wordpress Accounts at all unless you have something else that requires Wordpress Access. If you log out from here, and access that link again, you will still see the comments, but you will be prompted to log in. Which will open NodeBBs login page in a new window, you then log in, that window closes and you're now authenticated.
After reading about nodebb-plugin-blog-comments, it's exactly what I'm looking for. You mentioned there is an option to push which is great! If I use nodebb on existing wordpress site, does that option appear for new posts or does it also apply to old post as well. What about old posts that already have comments?
Installation of the comments plugin is done by changing comments.php on your Wordpress theme, so all calls to your existing comments would be removed (the comments would still exist, but in your wordpress database not NodeBBs) this may sound complicated to explain, but you have a few options here. You could alter the code so that it displays both comment engines, then turn off commenting for wordpress, however your wordpress comments wouldn't be transferred to NodeBB. You could wait for
nodebb-plugin-import-wordpress to be ready, and fork it so that it only transfers blog comments to the created topics, however your mileage would vary on that. As it's not been tried.
The option to push is available if you're an Admin of both Wordpress and your Forum, or you can allow other sites not controlled by you to use your comment platform by making them a "publisher" in your forum groups. (They would be an Admin on their Wordpress site, and a publisher on yours) You can push any topics to NodeBB, new & old, and a new topic will be created.
The plugin developer @psychobunny did mention that the plugin could do with some reworking, though he's unlikely to admit he said that.