With plants, it is not uncommon for seemingly unrelated characteristics to be linked in their DNA. For instance, wild male Kentucky Coffee trees are tall and lanky, while female trees are a bit shorter, wider growing and fully branched. So one explanation might be that white and pink color expressions are linked to smaller overall plant size (or some other characteristic that causes shorter growth).
Being of horticultural standing, though, this may or may not be the case here. Given that there is wide hybridization of Hyacinthoides in horticulture, it's difficult to say whether Calsurf's and Dasyl's are indeed the exact same true species. Comparing their respective outcomes might not be so telling. There are (minimally) two more explanations.
The particular plant clones that Calsurf bought may have just been variations in the species that genetically programmed to grow shorter and taller. In other words, that's just the way they are. (Different from the first example as there would be no DNA linking here.) Or perhaps the white and pink versions were previously infected with a virus or virus-like organism(s) that is keeping them shorter. Viruses do not always kill, and in fact more often live in commune with the host plant.
