There are tactful ways of letting someone know that there might be a problem with their script. A simple statement of fact, delivered neutrally, should suffice. "I ran the script and noticed that it used a lot of memory", rather than "I ran your script and noticed that it used a lot of memory."

If you're feeling charitable (and confident that your boss wouldn't object), you can add "I have some experience with tracking down memory leaks in Perl. Would you like me to take a look?". If no, drop the issue and move on.