Because I can't just let someone be wrong on the Internet: This does mean what you think and is certainly not a translation error. There is no real equivalent to "advanced degree", meaning MS or PhD, in German that could have been mistranslated. German job adverts instead usually say something like "Hochschulabschluss" (university degree) and specify if e.g. a PhD is preferred. Additionally, since "exzellent" is a German word that means... excellent, there is little chance someone would mistakenly use the English word to mean something else entirely.
In fact, job adverts calling for "above average" or "very good" degrees, especially in research oriented graduate roles, are common. What exactly that means varies from employer to employer, it just indicates that they care about your academic performance, not that they would outright reject you for not having a summa cum laude PhD.