Yeah, it looks like the normal ridge formed by the squamosal and parietal bones along the rear edge of the skull:
- http://academic.emporia.edu/sievertl/verstruc/ALLSKULL.HTM
- https://campus.murraystate.edu/faculty/tderting/anatomyatlas/settle1.html
- http://journals.usamvcluj.ro/index.php/veterinary/article/viewFile/9604/8540
You can even see the same ridge on other photos (it’s just their necks are “beefier” or at a different angle, so the “gap” isn’t always as pronounced):
1.https://www.inaturalist.org/observations/13157476
2. https://www.inaturalist.org/observations/9487484