'An extract is “cast” by drinking it, as if imbibing a potion'
If you are getting hung up on this, perhaps you should read this:
"It is a standard action to use an extract, mutagen, or throw a bomb. This action includes retrieving the necessary materials from the alchemist's supplies, in the same manner as retrieving a material component is included in the act of spell casting."
Drinking a potion DOES NOT "include retrieving the necessary materials from the alchemist's supplies, in the same manner as retrieving a material component is included in the act of spell casting."
Therefore, when combining ALL of the text regarding an extract specifically, it reads:
"An extract is 'cast' by drinking it, as if imbibing a potion. It is a standard action to use an extract, mutagen, or throw a bomb. This action includes retrieving the necessary materials from the alchemist's supplies, in the same manner as retrieving a material component is included in the act of spell casting."
That IS NOT the same as drinking a potion, it simply involves putting it into your mouth, the same as you put potions.. or tacos for that matter.. in your mouth. Furthermore, nowhere in that text does it explicitly state that extracts provoke AOOs.
Extracts are Su magical items, they are not potions. It might seem counter intuitive, pathfinder has many quirks and nuances, but using extracts does NOT provoke AOO.