These terms are a generalizations vs representing specific cause and effect.
I would think of 'seedling' stage as a substage of vegetative phase, but that sort of thing is a bit arbitrary.
Also, after flip to flower, the plant still grows leaves and elongating stems (a.k.a. "vegetative" growth) for 3-4+ weeks. so, you have 'vege' growth in flower phase, too. They could have categorized this as some transition or 3rd phase, but arbitrarily it was not organized that way. Maybe, in more advanced classes they do expand on those basic stages, i wouldn't know.