That is excessive for what you discribed. You didn't say if the rotor was turned or replaced as I suppose some break- in will create more dust. The culprit is likely pad quality though I'm not familiar with the pad you used I can say that from my own experience when it comes to the auto parts chains I'll only use ceramic pads. All the others make too much black dust.
I've run into the same problem on my motorcycles that have disc brakes whenever I use the cheap aftermarket pads rather than the Brembo ones my Moto Guzzi and BMW call for.It's cheap lining material. The ceramic ones seem to work better.
