I guess the truly telling point would be: can a Squib make potions? If they can, then it would indicate that the magic involved is in the ingredients and the spell book that defines the process, and that all that is truly required is to be enough part of the wizarding world to be admitted to Diagon Alley to buy yourself a cauldron, a book of spells, and the right ingredients. And practice, practice, practice. In other words, a learned process.

But if making a potion is beyond the capabilities of even the most determined of Squibs, then there is extra magic involved in the process of making it... and there's more to it than just learning to be a good cook.