This predicate does not really create a file, it just creates a unique name for a file in `/tmp`

For example:

?- tmp_file(mine, F).
F = '/tmp/swipl_mine_10397_0'.

That file doesn't exist at the time the operating system was queried but may exist in a millisecond. Or may be a link, or a directory. If you regard the filesystem as a database (which it is), following this up with a file creation is a transaction-less hail-mary operation.

10397 is the process id of "swipl" btw.

On Unix/Linux, this is certainly performing a call to the mktemp(3) function:

https://linux.die.net/man/3/mktemp

where we read:

Never use mktemp(). Some implementations follow 4.3BSD and replace XXXXXX (of the
template name, which cannot be given in this predicate) by the current process ID and
a single letter, so that at most 26 different names can be returned. Since on the one
hand the names are easy to guess, and on the other hand there is a race between
testing whether the name exists and opening the file, every use of mktemp() is a
security risk. The race is avoided by mkstemp(3).

Or you have to tune the "tmp directory", which is `/tmp` here, to be a directory under your control. See tmp_file_stream/3 for that.

This predicate can do something that tmp_file_stream/3` cannot do: it can create temporary directories. For example:

?- tmp_file(swi, Dir), make_directory(Dir).