This is an epidural hemorrhage, as noted by the biconvex shaped hematoma on CT. Epidural hemorrhages are due to rupture of the middle meningeal arteries (FA2020 p513) Epidural hematomas commonly have loss of consciousness, then a lucid interval before quick decline to coma.

Shearing of the bridging veins occurs in subdural bleeds. Subdural hematomas present as a "crescent moon" shape on CT. Seen in shaken baby syndrome.

Subarachnoid hemorrhage is usually caused by rupture of a saccular aneurysm or AV malformation and leads to the "worst headache of my life" and blood molding to the cerebral sulci. The sigmoid and transverse sinuses are dural venous sinuses. Dural venous sinus thrombosis with secondary venous hypertension can cause subarachnoid bleed but is rare.

Bleeding from the lenticulostriate arteries presents as an intraparenchymal hemorrhage within the basal ganglia ans is commonly due to hypertension. These would present as hypodense areas within the brain tissue rather than on the exterior.

If you need more convincing that this is an Epidural hematoma, note that the blood collection does not cross the suture lines. Compare against subdural hematoma which does cross the suture lines and can be seen creeping along the length of the inner surface of the skull. Pictures in First Aid show good examples. (FA 2018 pg 497)