His answer is rules as written. Sage advice is rules as intended. Easiest way to explain it.

Example. you are a level 4 fighter level 5 rogue. You would lose a level of rogue, losing everything you would have gained for being a level 5 rogue. As you now are equivalent level 8 you would also loose your feat gained at level 9. Most people do not record exactly where the placed skill ranks per level and as such this will allow for fair and balanced removal of ranks. If you have recorded everything then the appropriate course of action is to undo everything you gained when you last leveled your highest level class.