I mean, the evolution of Cetacea is fairly well understood by now. We know they all derive from a terrestrial small carnivorous artiodactyle. And all descendants had sharp teeth until relatively recently. Even today quite many of them are still active predators.
This particular finding seems to be about early baleen whales, back when they still had teeth (not just baleen). Seems like early baleen wales had very sharp teeth that were likely used for cutting, not for some sort of early type of filtration.
You might be interested in the actual paper: http://rsbl.royalsocietypublishing.org/content/13/8/20170348