What I'm saying is this. You're faced with various ways in which dust-based systems differ from ordinary ones (e.g., you can't interact with them). Then you have two options: either say dust-based systems don't perform computation; or say computation doesn't require interaction. The difference between the two is solely in the definition of "computation".

Discussing the appropriate definition of "computation" is a worthwhile discussion to have. But you have to be aware that you won't get any more information out of this deliberation than you put into it.