Red Mage Problem

[Lumivyory]

This is what it says:
Description
Use this item and learn everything you need to begin your adventure as a level 70 red mage.
This item will instantly level red mage to 70 and complete all job quests up through "With Heart and Steel."

Exactly, it says "all JOB quests". Job quests are basically necessary side quests that allow you to learn more skills and learn more about your job. And those quests were skipped when you used the boost.
Main Story Quests are exactly what their name is - main quests of the game. Those can only be skipped by using an MSQ skip which is not the same as lvl 70 job boost.