Such thinking is often based on the silly belief that all people are early to bed, early to rise.
Many of us have never been that.
Was I 'demented' when I would scribble away my frustrations in my diary at 2am as a teenager? Was I 'demented' because I stayed up late when I would play Rage Against the Machine on my stereo at that hour as a young adult? Was I demented when I would awaken my ex at 3 am to run to the grocer and get me a pint of ice cream, because I was pregnant and I'd just awakened for the third time that night to go to the bathroom? Or was I demented at 3 am when I was manning a widget machine at my graveyard shift job as an older adult?
Not in the least. I was simply awake at what other people call the middle of the night, for a variety of reasons, none of them having anything to do with dementia.
I'm not defending the idiot's vitriol, but that the hour of it doesn't have a discernible cause. It could be a sign of dementia. Or it could simply be someone who's a night owl. Or someone who has a bladder control problem waking him up, as some older people do.
Plus, some older people simply don't sleep all that much, demented or not. My mum, who was a traditional early to bed/rise type most of her life, now keeps the weirdest hours in her advanced years. She's older than this idiot, and hasn't one sign of dementia. Nevertheless, she's up at all hours now. I get calls from her at 2 or 3 am, because she's lonely and knows I'm there to talk to--because I've *always* been the type to be up at that hour, left to my own devices.