Hi! In the thread that you reference, the reporter is having trouble with the number of threads that the elasticsearch user can create:
This message is arising from the maximum number of threads bootstrap check. For Elasticsearch not running under systemd as a service, this limit is controlled by the nproc limit. This is why I refer the user to nproc there.
However, the page that you refer to regarding nofile is referring to a different issue. Namely the fact that the elasticsearch user also needs the ability to have a lot of file descriptors open. This is covered in the file descriptor bootstrap check. For Elasticsearch not running under systemd as a service, this limit is controlled by the nofile limit.
In short: the issue the user is running into is different than the situation covered by the docs that you link to.
I hope that helps!