This makes total sense.
Just because your marijuana collective is huge -- here, 1600 people -- doesn't mean that it's not a legitimate collective. The trial court's contrary holding gets it wrong. So the Court of Appeal is required to reverse the conviction.
But Justice Benke's opinion is equally right that the size of the collective is relevant to whether it's a legitimate collective or instead merely operates to make money. So a jury could legitimately find that the size of the collective made it more likely that it was designed for profit rather than merely to give a means for members of the collective to obtain access to their medicine. As a result, a trial court should instruct the jury accordingly on remand.
I think that's exactly right. A jury could decide that it's a fake based on the number of participants. But a jury could reasonably go the other way as well.
(Ditto, by the way, for the presence/absence of financial records, corporate minutes, etc. All of this is relevant to whether it's a legitimate medicinal enterprise.)