That would be my guess, that she was exposed to a split roo before you got her. If you get the same thing out of her after she is with the fluffy roo at your house for a month then I might think differently.
So far we've seen what would be expected of a simple recessive trait. These birds were crossed with a silkie to check and they definitely carry the same gene. I wouldn't say 5 chicks is enough to say anything odd is going on...just the luck of the draw since each egg had a 50% chance of being smooth. Just like families with 5 kids that are all one gender...nothing funny going on, just luck of the draw.
That would make sense if there were split roos in the pen too. Maybe they were younger and she probably thought they weren't breeding yet. Sometimes those boys can be sneaky!