The dead we can imagine to be anything at all

My grandmother liked to say my brother Dimitri would have been a great painter but that was only because Dimitri was dead. The dead we can imagine to be anything at all.

Source: Bel Canto

Background: The grandmother was saying that the brothers could have been an artists, especially Dimitri who had died young.

I don't quite understand the highlighted sentence. Does it mean "Anything could have been possible because he was dead and nothing can be proved." Thanks