Kevin,
If when the AF is activated by a half-press of the shutter release button, the button is held in this position, the point of focus will not change when the button is pressed fully to take the picture. Holding the button halfway down and keeping it there locks the AF at the point the lock was obtained. Releasing the button and then recomposing would do as you say.
I quite often use the technique the photographer you met was using, it helps ensure the bit you want to be in focus is the point the camera choses. If you leave it entirely up to the camera, it may pick a point you don't want to be the main point of interest.
The trick is to keep the button half pressed when recomposing. If you read the manual for your camera it will describe this feature.
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