that's definetely a krausen. the krausen really isn't a good indicator, either. the only way to know for sure is with a hydrometer, and even that will only tell you when it's done with it's primary fermentation, NOT when the yeasts are done cleaning up after themselves.
Whenever in doubt, leave it an addtional week, i say. I've found the longer i leave my beers in the carboys, the better they usually turn out!