You've (probably) installed Bolt in the wrong folder.
It's recommended to install Bolt outside the so-called web root, because this is generally seen as 'best practice', and it is good for overall security. The reason you are seeing this page, is that your web server is currently serving the incorrect folder as 'web root'. Or, to put it the other way around: This file should not be visible.
The current folder is:
The best and easiest fix for this, is to configure the webserver to use
/home/johncube/public_html/dev/muzikantendag/public/ as the 'document root'.
Alternatively, move everything 'up' one level. So instead of extracting
.tgz file in this folder, extract
/home/johncube/public_html/dev/ instead. If you do
this, you must edit the
.bolt.yml file as follows, so it use
the correct folder.
paths: web: "%site%/muzikantendag "TIP: copy this snippet now, because you won't see it anymore, after moving the files.