They had cast Pass Without Trace and had ungodly high Stealth, so they weren't noticed until they got into the Winery.
The combat with the 24 twig blights and 1 druid in the fermentation room was over before anyone could've heard or gotten there (less than 2 rounds). And even if they would have joined the fight, we have two issues...
1) The area was too small to accommodate the creatures already there, much less adding more fodder.
2) The HP, attack bonuses, etc., are still too low to challenge the party.
The party hasn't yet left the Winery, so they will have to deal with the 30 blights outside now. (Of course, they can safely rest inside and go completely nova on the blights the next morning.)