It's easy for a crawler to parse a robots.txt in different ways. The article say...

		txutxu on Oct 19, 2013 \| parent \| context \| favorite \| on: Who exactly is crawling my site? It's easy for a crawler to parse a robots.txt in different ways. The article says to whitelist a few and deny everything else. The crawler could parse that, and change the user agent to one whitelisted on further requests.