A) This is a random opinion from the cafe
B) It literally says it can be performed impromptu, not that the trick in and of itself is impromptu.
C) Let's take that as the actual definition. Look at it from this angle:
If you did not expect to perform it, why would you carry the gimmick around with you. Especially something like Bottled, which utilizes a specific scenario (which would be borrowing an empty
plastic bottle, one that the spectator is about to throw away, or about to finish, with a specific kind of lid/brand). This is a very specific scenario. No one would carry a gimmick with them in hopes for a specific scenario like this to arise.
I get what you are saying: From a layman's point of view, the trick looks impromptu. At the same time, so should a lot of your other tricks, right? I mean, Angle Z should be made to look 100% impromptu, even though it isn't (I mean, except for the impromptu version). Furthermore, you aren't marketing this to laymen, you are selling it to other magicians, so it should not be referred to as impromptu unless it is truly impromptu. In fact, I would not mind if it is marketed as semi or almost impromptu if it truly required only a one time or easy on the spot set up. However, to market something as impromptu is completely different as an impromptu trick.