I haven't read the article, but, it sounds like it happened during the picking process. Because produce is picked fresh and bagged on site lots of creatures can end up in bags of lettuce and other packaged on-site products. That's my guess. Now, I'll go read the article.
OK - read the article and agreed - someone put this in the broccoli after it was cooked and I'm with Scotch on this one - investigate the patron first.