This package installs Discourse without Docker, for several reasons (mostly to support ARM architecture and low-profile servers, to mutualize nginx/postgresql/redis services and to simplify e-mail setup). As stated by the Discourse team:
The only officially supported installs of Discourse are Docker based. You must have SSH access to a 64-bit Linux server with Docker support. We regret that we cannot support any other methods of installation including cpanel, plesk, webmin, etc.
So please have this in mind when considering asking for Discourse support.
I found some more written down reasons for Yunohost not wanting to use Docker :