but I wonder how it can contain sufficient fuel for landing in that size vehicle.

The amount of fuel it would need for the final landing is not so large.

and, though NASA doesn't seem to be specific, calculations show it was probably under 250 mph - I was surprised it was that low (I thought it would be dropping like a rock). So I guess it doesn't take that much fuel after all - though their "can land as precisely as a helicopter" must mean they start some rockets well before for steering, rather than just simple slowing down.

Dumping it all into white heat. I would soil myself.

So a rough estimate is that the fuel energy required is comparable to the energy a parachute dissipates during descent.

BTW, it still retains a parachute as a backup. It does a check when it's time to fire the engines and deploys a parachute if there's an indication that the rockets might not work.