Bimmers expressions often remind me of Buster. Maybe thats why.
And how you describe him not quite being dog like. Buster is like that, he lives in his own head. I know him the best of anyone and I feel I barely know parts of him, we'll often find him just sitting alone apparently thinking to himself.
I find him incredibly emotional and reserved, more like a furry little person than anything else. I wish you could meet him, I think you'd like to get to know him.