Well mostly because of how it’s mouth is shaped like a right whale’s but… a lot smaller. The people who named it were using a little piece of baleen and a glimpse of a live animal to give it it’s name.
Notice the curve of the upper jaw and how the lower jaw lips come up to meet the upper jaw – much like a right whale’s.
Scientists are slowly learning more about the pygmy right whale through post mortems (like this) but as they don’t wash up on beaches very often, not many have been done.
This is why this dissection over the next couple of days is so important to the scientific community. There is so much we simply do not know about this animal.