I noticed these lines on your logs:
Could you check if you have two conflicting nginx processes or any other process is binding port 80 already?
The nginx configuration file is fine (some characters are missing such as ‘\’ I guess due to html escaping when pasting).
By the way the guide Passbolt v1 on CentOS 7 with NGINX / PHP7-FPM / MariaDB from scratch | by Kevin Muller | Medium has been updated with more accurate centos specifics. I would recommend to take a look on the updated version of the guide, follow the new procedure from scratch and if you experience problems again update this post.