Nothing wrong with that. The might have included a little more detail. The reason it's rough is that the fuel air mixture is not even for each cylinder, some tend to be leaner than others, as you lean, the leanest one will reach the point where it's too lean to for combustion, so that cylinder stops producing power, and the engine runs rough because it's running on 5 cylinders instead of 6, just like if you'd pulled off a sparkplug lead.