I've read that the pouf is the result of the skull having a 'hole' in it...and the pouf can be anywhere...centered or off to one side or the other. Just look up Crested ducks and there is a lot of info out there on them. 2 crested genes end up being lethal to the duckling growing in an egg, so they don't make it I guess. The ones who do survive have the gene from 1 parent (I think.) I've got my original blue and black Swedish pair and she is crested and he in not. We have babies (grown up) with the crest and without it.
Either way, they are cute! I think yours is definitely Black Swedish, possibly mixed with something else, or not. 2 of my Swedish ducks, the original Blue Mama, is getting more and more white all over her head and back. One of her black babies feathered in with so much white...not just on the chest, but on the face, head and back too.
Have fun with it- whatever it is.