My Father (70M) Having Random Delusions, But Otherwise Fine?

I'm familiar with dementia. I took care of my grandmother for almost six years who had dementia.

My father is a weird case. I'm not sure if he's showing early signs of dementia, or has developed some kind of mental illness.

Twice in the past 12 months he's fallen for a fake celebrity romance scam.

Last spring he thought Sandra Bullock was messaging him and they were dating. This wasn't in his head, there was someone pretending to be her talking to him.

Now it's Olivia Rodrigo. He told me today that he's been talking to her for well over a month, and he wasn't supposed to tell anyone. He wanted to let me know though because she's sending him a private jet tomorrow to take him to LA to live with her, and he said he'd feel guilty if he just disappeared on me.

Apparently one of the most famous pop stars in the world right now at 22 years old wants to date an overweight, alcoholic 70 year old man who is destitute and lives in a rooming house with not a single asset.

What's weird to me is I see my father 5-7 days per week. These are the ONLY two instances I've seen him being completely delusional. He can carry a conversation, he can talk in depth about topics he knows, his long and short term memory are perfectly fine, he can do math, he can solve problems, etc.

His age and his lifetime of alcohol abuse have made me wonder if these are early signs of dementia, but the fact I see him as much as I do, and I know these have only been two incidences, I wonder if it's maybe the manifestation of some kind of mental illness?

My father has never been formally diagnosed with anything, but looking back to my childhood it wouldn't surprise me if he had some mild form of bipolar disorder. Maybe his age and drinking have just started it to sometimes manifest more seriously sometimes when he's in a manic stage.

Anyone have any thoughts? Dementia? Mental illness?