Sorry, I don't have horselords so I wouldn't know about nomad nonsense. That sounds buggy. It doesn't really make sense that a holding can have separate tech from a county, since holdings per se don't normally have technology. It would be bizarre if that's WAD.
I'm not sure honestly, I could see how it could be WAD; if you camp in a clear stretch of grassland inside Constantinople with your nomadic steppe horde and keep to yourself, you don't inmediately become a cultured Byzantine ruler, because your nomadic way of life prevents you from adapting that quickly to the environment. And it would make sense that your technology levels were mantained when you change capital; the improvement in the capital holding are not lost, so I guess in game terms it always was the exact same place, just located on different points as you moved the capital around.
Or it might be a bug after all.