Yes, that description is fairly ambiguous, and sailing downwind well is a combination of steering and trimming, but I think what he is getting at is whether the crew adjusts the jib or not. On sloop-rigged boats, where you aren't trying to do the wild-thing downwind, you usually set the mainsheet and don't touch it much. So you can either steer to keep the jib flowing or trim the jib to keep it flowing.
In reality, you should do both. As the wind direction changes or the boat changes speed, the apparant wind will shift causing the jib to luff or stall. Usually the jib can be trimmed faster and more smoothly than the boat can be turned. Tell the crew to concentrate on keeping the jib flowing while you steer to keep the boat powered up and surfing if possible.

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