It hadnt actually occurred to me, but mum does that too - lining up the cutlery so that the bottom of the handles come to just the edge of the table.
I have been told that OCD often occurs when the person in question feels like they have no control over anything in their life and that it is a way of gaining control over something. I suppose that it would make sense for the dementia sufferer to try and regain some form of control.
Bill does that with the cutlery too. That's an interesting thought Canary.