These dwarf French beans are known commonly as black calypso beans, yin yang beans or, as Meighan illustrates, orca beans. Despite the group broadly being called French beans, the genetic origins of this kind of bean are in Central and South America. The English moniker of French bean is due to an association of where they first became popular in Europe.
I’ve tried to track down the origin of this specific cultivar, as there is conflicting information online (with many references to it being a heritage cultivar). The source I most lean toward trusting is the 2004 book Beans by Aliza Green (there’s a limerick there, somewhere), where she writes: “This boutique bean…was developed by growers in Europe, where it’s become quite popular”. The Royal Horticultural Society’s Horticultural Database (linked above) notes an illustration of the cultivar in The Garden from 2002; I’ve looked at that issue and ‘Yin Yang’ dwarf French bean appears under the headline “Exciting New Cultivars”. This seems to conflict with what I would consider a heritage cultivar, though even if it strictly isn’t, it is still an intriguing and fun bean.