it's about the projected length of the outcome. Projects according to GTD are multi-step, but still with a rather short timespan (from a few days to three months?).
Goals would be longer, larger and contain many projects inside them ( timespan would be anything from three months to a lifetime depending on your "altitude")
It's all explained in the GTD book, so you may want to re-read it. Semantics are sometimes a bit confusing. Objective, goal and desired outcome mean the same thing - something you desire and are willing to labor to get it. Someone once called goals as dreams with a plan and a timetable. A project is a useful abstract concept in planning stages.
So even Tracy's single goal would contain hundreds of little projects...