Your father, in his grief, connected two unrelated events.
People do all kinds of things when grieving, but carrying it on so long is absurd. I mean it is really silly, isn't it. The only thing those two separate events have in common is that they happened on the same day. Many other things happened on that day too, and all of these events are separate and unrelated.

Linking these two things is riduculous. The absurdity of it is laughable. What others believe, what they think, is only about them. Nothing more.

Don't let it in. Reject it as invalid and irrational which it is. It is so irrational that there is no trying to explain why someone could think it and could believe it at all, and especially for so long a time.

I can think, and say, and believe that the sky is green.... but it doesn't make it so.