More than likely, it's an artifact of code that's been modified by someone who didn't notice that he no longer had a list to join together.

Maybe the original code was slurping a file into an array, as in

...at which point

...would make sense. As the code evolved, its author grabbed the webpage from the website with LWP::Simple instead of slurping in a file, and the code got modified, but not quite enough to eliminate the useless use of join. ;)