What I said is true and I think that I covered your case with:

Once you have given execute permission to the file, you can just type "helloword.pl" and it will run. Typing "perl helloworld.pl" explicitly starts the Perl interpreter and sends it the helloworld.pl file.

You said it was required to set execute permission. It isn't. Now the phrasing of the lines above is such that for someone unfamiliar with permission bits, it still looks like "perl helloworld.pl" requires execute permission.

Also note that you can just type "helloword.pl" and it will run only works if either . (a dot) or the path of your current directory is in your $PATH. Given the example case from the book, the latter is very unlikely - and putting . in your path is usually strongly adviced against.