From the article:
However, despite treatment, in the 14 days following an aneurysmal subarachnoid hemorrhage, many patients may develop worsening symptoms (such as speech problems or difficulty moving). This is caused by blood from the initial stroke irritating blood vessels, causing them to constrict enough to cut off the blood supply to a portion of the brain (called a vasospasm), resulting in more brain damage. This complication, called delayed cerebral ischemia, is a leading cause of death and disability after an aSAH [aneurysmal subarachnoid hemorrhage] stroke.
[…]
After adjusting for several patient characteristics as well as recent exposure to other illicit substances, patients who tested positive for THC at last follow up were found to be: 2.7 times more likely to develop delayed cerebral ischemia; 2.8 times more likely to have long-term moderate to severe physical disability; and 2.2 times more likely to die.
[…]
The study does not specifically address how cannabis raises the risk of vasospasm and delayed cerebral ischemia. Lawton noted, “Cannabis may impair oxygen metabolization and energy production within cells. When stressed by a ruptured aneurysm, the cells are much more vulnerable to changes that affect the delivery of oxygen and the flow of blood to the brain.”