Your server is running PHP version 5.3.29 but WordPress 5.2.1 requires at least 5.6.20.
This error message is the entire contents returned by the server when you go to the home page of the website. "Do not adjust your screens, we control the vertical, we control the horizontal."
The error is self-explanatory; the administrators of this website are running incompatible versions of software. The administrators need to fix this. Or not.
A worldwide-web server is a "stack" of software. Here in the forum section, they are probably running: Apache webserver to format and "serve" you the web pages you ask for, mySQL relational database to store all the stuff we've typed in + configuration stuff like our passwords & which posts are unread, php which is an easy to understand programming language that here basically extends what the web pages can do, and phpBB which is a complex forum software package written in php, that does most of the heavy lifting.
phpBB doesn't reference any WordPress scripts so that is why you don't see the error here.
My laptop is running php 7.2.17-0, so you can see the version of php they are using is very old. The version of phpBB is also very old.
There is a help and site issues thread under general, but since I am prevented from writing to it I'm not going to worry about it. And it hasn't been updated since 2015!!