My DH has a mild case of Asperger's. The beauty of it is that what you see is what you get. There is no hidden agenda or maleficient strategy. The other beauty of it is that I can be very direct with him and he won't ever get offended. He is also very resilient, since he doesn't collapse with the weight of his feelings
The sad part is that he sees the world in black and white. For every problem, there is a solution. If not, then it's not a problem. See how he thinks? That leaves no room for just listening and empathizing.
So there is really nothing to understand. You have to keep your interactions to practical matters. You could have said: "The rule is that you never throw out anything your grandchildren give you until they're out of your house." Aspies love rules!
They also hate change and transitions, but that's also a consequence of aging as well. So even if he wasn't Aspie, he might still not want to move.
Always use rational and objective arguments when arguing anything with him. The emotional stuff doesn't fly.