tmp at the root of the hosting account is not a real directory, but symbolic link (symlink) to the system directory
.system/tmp, which stores temporary files created by site scripts in the course of their work. That is, when opening a directory
tmp actually the contents of the directory are displayed
This symlink is intended so that, if necessary, you can quickly get into the directory with temporary files, check or clear its contents using file manager or any FTP client... Previously get into this directory by FTP could only be instructions.
Removing this symlink does not affect the operation of sites in any way. After a while, it will be automatically restored.