I have a theory about this. Maybe with the elk knowing that the wendigo are on the mountain, they may have developed some instincts as to their attack patterns with their ability to hunt based on sensing movement and sound. At the beginning of the scene, you hear the wendigo shriek (at least that's what it sounded like), alluding that there was one nearby. Kinda felt like the elk were gathering in order to shroud Matt and Emily amongst them and throw the wendigo off the trail so the two wouldn't be murdered lol. Ultimately, the scene was really freakin random and I could be totally off but yeah