Yeah, that was it. Solved it myself. Only took like 6 hours. I hate Apache configuration so much ...
Here is the final solution for others in similar predicament:
How to remove ":4567" from your address properly with Apache + mod_rewrite.htaccess:
RewriteCond %{HTTP_HOST}%{REQUEST_URI} ^some.example.com/index.html
RewriteRule ^(.*)$ http://some.example.com:4567/ [NC,P,L]
RewriteCond %{HTTP_HOST} ^some.example.com
RewriteRule ^(.*)$ http://some.example.com:4567/$1 [NC,P,L]
Just replace the bolded addresses with your own domain, add into your root level .htaccess file and turn RewriteEngine on.
Explanation of what happens here:
The first line matches your address and if it contains some.example.com/ or some.example.com/index.html it replaces it with (on the seconds line) with some.example.com:4567
(without these two lines you will get errors when you try to display the main page because Apache adds "index.html" by default to the request which gets then handled by Nodebb because of the two lines below these first two - but there is no index.html to handle because of the way Nodebb is built)
NC = ignore case
P = proxy, so that it is invisible to the user (they don't see the :4567)
L = last rule, we stop if match is found
Third line matches only your host without the trailing /somepage.html or /images/someimage.png or what ever. And the last line replaces that with some.example.com:4567/ and adds the rest of the address with $1
This is rather useful if you are already running other websites besides the Nodebb forums with Apache on the same server. Because if you use the instructions in the documentation for ProxyPass you will get all of your web traffic rerouted with that configuration (unless you are running Nodebb from a subfolder, I think?)
Well, I hope this is of some use.
And remember to edit your config.json:
"url": "http://some.example.com",
"port": "4567",
If you find errors in any of this please post here.
