Yes, Nginx and HHVM are running (this last one in socket mode) and I explicitly commented the line in the config for the server port. Error log files for Nginx and HHVM are empty.
It returns a 502 bad gateway when I visit a file ending in .php or .hh, EVEN if it doesn't exist.
I have followed the SAME tutorial here: https://community.nodebb.org/topic/11032/nodebb-full-stack-setup (Linux Ubuntu 16.04.3 LTS) and service hhvm status and service nginx status are up, loaded, running. HHVM works in CLI as php command and even returns the version HipHop if I add the -v parameter.
PHP-FPM is NOT installed.