The article makes it sound like it doesn't matter what size or mass.
Parameters: Radius 650m, Circumference 4084m, Period 7560s, Speed 0.5157m/s, Mass 2.1e12kg
The numbers are so small that if you take the speed they are moving of 0.5157m/s tangental to the surface and point it straight upwards and accelerate it with the gravity of 0.0003315m/s/s then it would come to a stand-still in somewhere over 1600seconds at a height somewhere over 800m and fall back towards the asteroid.
I don't know the maths to figure out the exact values since they vary so greatly with distance, but the difference in centrifugal and gravitational force is only 0.00007765m/s/s. That means that something weighing 100 TONS on earth would have a net upward force of about 1.6 pounds. Of course you can't treat the asteroid as discrete frictionless atoms. What holds a dirt clod together overcoming the full force of earth's gravity to maintain it's shape?
So if you were attached to the surface and dropped a rock it seems to me that it should continue upwards and orbit the asteroid at some altitude. It doesn't surprise me though that since dust can stick to my ceiling and ceiling fan blades even when they're whirring around that this asteroid can stick together.