re: Is it just me?
It's not you Scott.
It's hypothetical.
They wanted to plug Ion drive which is a reality against gravity generators which are not real, as far as I know.
That ships mass would not be near enough to tow an asteroid.
I think they are imagining a gravity generator.
I kinda like the engine thrust layout.
I wonder if there are nozzles all the way around, there don't appear to be.
http://antwrp.gsfc.nasa.gov/apod/