Ah, so it's more a Chrome feature than a Google (Search) feature. Chrome is parsing the URL for that bookmark and responding accordingly - it's basically dynamic bookmark creation, with custom styling. Seems like a nice idea, could make a cool standard.
Pretty neat way of implementing this without compromising security imo. It would be nice to see this on other browsers as well since it could make finding shared text snippets much easier for the person receiving it outside of Google.