strange setup of site at least to me… can't figure this out…

OK, first, I’m not a WP guy I’m a Joomla guy and learning as I go so please bear with me.

I’m coming in on a webiste that I didn’t build. The directory structure is odd to me. There is a WP install at https://www.example.com and if I go to the admin for that https://www.example.com/wp-admin it immediately redirects to https://www.example.com/blog/wp-admin

So I FTPd in and looked at the file structure and sure enough, there is one install and then a sub directory called “blog” and inside that is another complete install of WP.

Anyone ever hear of this? And if this were Joomla I’d just use Akeeba backup and make a copy of the site, take everything out of the directory and then re-install it under the root directory and change the config.php file to reflect this and the site would be fine. What is the process for a WP site like that?