Can someone get delirious due to high blood pressure? What if the person has recently had a mild brain stroke?

My Grandfather has had a mild brain stroke. This has left him partially paralyzed in the left leg and left hand. He's been making good progress moving his leg to the point where he can now walk with a cane after only two months. Doctors say he'll get better in the next 5 to 6 months and will be able to walk without a cane. His speech centers are intact and he has no problem with logic and thinking and speaking (a bit slurred but getting better). However, yesterday, for the first time he all of a sudden started talking about things that didn't exist.....My question is, could this be because of the stroke or because his blood pressure seemed to be high on that day?