Not totally sure about the "Tradition" designation, but in the past when Guntrum has used that (and when there's not an accompanying designation of variety on the label) it was to signifiy that only the 'traditional grapes' are used...and are almost certainly blended.
What that means is the bottle you had could have been made from any blend of Riesling, Sylvaner, and Kerner...and there's probably a good deal of Sylvaner and Kerner, I'm guessing.
But that's just an educated guess (or WAG, really), based on the fact that I've had some Gunrtrum Sylvaner sweetie-pies before, and partly on the knowledge that a lot of the sweet wine makers have been playing around with Kerner since the 1970s, especially in the Rheinhessen and the Pfalz, because it makes big, fat, glossy sweet wines pretty well.
Guntrum for a goodly while has been trying to simplify the labelling miasma for non-German drinkers (and a few younger German drinkers, for that matter), to make their wines more approachable and sellable. Unfortunately, for such an old estate family, they've also been engaged in dumbing down a lot of their wines too. But they have some tremendous vineyards on the slopes of the Rhine, and make some killer Riesling wines, labeled as Nierstein and Oppenheim. They are on a gorgeous (both scenically and viticulturally) place called the Rhein-Terasse.
Good place for wines, castle viewing, boat tours, and essen und trinken mit geschmackt!