The Kraftfahrt-Bundesamt says it takes into account a number of Abgrenzungskriterien including size, weight, performance, seating capacity, # of doors; however it has no standard formula for assigning Models to a Fahrzeugsegment. The only criteria used that truly differentiates the segments is price. If you take a look at the vehicles included in the Oberklasse segment you quickly see a pattern, they're all really expensive.

If you asked a 5 year old to play "which one of these is not like they other" they'd quickly zero in on the Tesla models very quickly because they don't look like luxury vehicles. That's not to say that the Tesla models aren't very nice cars, they're just not opulent. The Tesla models cost as much as they do because of the technology under the covers. The other cars in the Oberklasse segment aren't technologically expensive, they're pretty bog standard high performance vehicles slathered in expensive and exotic materials and refinements.