That's half right, which I guess is pretty good for a service writer!

The computer does indeed adjust the timing as you drive. It has a certain range of computerized adjustment to compensate for fuel, temperature, etc. However, there is a mechanical "base" setting that is adjusted at the distributor. if the mechanical setting is off enough then the computer can't fully compensate and you may have driveability problems or the like.

I don't know if that's the best way to describe it, but hopefully that makes sense. If you ever have a problem with something like that at the dealer just ask them why the service manual has instructions for setting the timing manually with a timing light!