There are plenty of creatures in Askamar that look like dragons. The yuynari are based on wyverns, while the bantagri were originally inspired by wingless dragons (although everyone who sees them insists that there is nothing remotely draconic about them now!)
So, why shouldn’t there also be creatures that resemble unicorns?
This is an elenya, or Askamaran unicorn. There are white elenyas in Barezeth, Imbire and Oumevare, and black elanyas in Quathevara and Drakazure (because I like black unicorns, too, and I can easily imagine them in the dark pine forests of those lands!)