Single comb is recessive so takes two copies to show so bred to a rose comb all would be rose but carry a gene for single.
But the rose comb could also be carrying a gene for single if that were the case it would be about 50/50 single and rose split to single.
IDK about 3rd generation because IDK what was meant with the first two generations.
Also don't know about producing all splash. There would be no reason it would unless it was splash laced bred to splash laced. It works just like any other BBS breeding.
Could of just been luck of the draw. Especially if only a few were hatched.