tcs...
I think you're simply dancing around it. An easy definition for mini-velo is any adult bike built around road or hybrid geometry that uses small diameter wheels.
That's what most people mean when they say mini-velo... so yes, a Moulton would fit into that category. However, a BMX bike would not fit as it's built around an entirely different geometry. Now... if you modded that BMX to the point where you changed the geometry then sure, you might have yourself a mini-velo.
--sam