Dementia-like episodes post stroke?

We are taking care of my FIL (70) who had his second stroke about 3 months ago.

According to BIL who was taking care of him for 2.5 months and kicked him out, he has some kind of demensia. Hallucinations, paranoia, etc...

He has only been in our care for a couple weeks at this point and has seemed generally "normal" as much as coule be expected. He can hold conversations and even partook in family game night amd helped bake a cake.

He does have some obvious cognitive decline, forgets things right away, obsessed with certain hang-ups, but generally seemed stable.

Tonight he seemed to have has a dementia-like episode. He complained that the electricity in his room didn't work (he had unplugged the power strip and plugged it into itself) then he came into the kitchen and started scooping out portions of the freshly baked cake from the inside out with a spoon, he also seemed incredibly sad/on the verge of tears.

This is very hard for me as I have no idea what he is experiencing or how to help him. I'm trying to be as patient and helpful as possible, but this kind of episode really concerns me.

Is this something normal for stroke survivors?