Until it's confirmed that it is or is not JVS or the Kalpoes' DNA, it's possible that one of the other girls staying in that room had a visitor over who may have impulsively picked up a toothbrush while in the bathroom just to clean some specks from his teeth, and the one he used just happened to have been Natalie's.
However, if it's determined that the DNA is in fact JVS or one of the Kalpoes, then there sure is a whole heck-of-a-lot of explaining to do...especially by those who were sharing that room with NH. It would then seem to me that there's another level/dimension to this story that's not been made public...just IMHO, of course, and assuming the DNA is one of the 3-amigos.