Yeah. And the cleric too.
The Passive Perception of the blights was a 9 ... no way that could fail.
Sorry. I don't think to check Jeremy Crawford's Twitter before every combat. But good to know for future reference.
But even so, fighting a mass of 30 twig blights would be another speed bump encounter.
Except what's good for the goose...
That druid can be sniped by the ranger in a turn, just like he was on the balcony in my game.
Also, I just took a look at the encounter.
Aren't the twig blights initially in a big cask, under total cover?
That means all the PCs see when sneaking into the room is 1 druid.
When they move to take out the druid, they're going to get mobbed by twig blights who should at least get 1 attack each in - causing some trouble. Heck might even be an opportunity for actual surprise (rare as that is) and the twig blights get 2 or so attacks in - causing some actual damage.
That's one thing you may want to be sure to look at carefully. Terrain is an often overlooked thing in 5e and, used well, it can make a big difference. And it can turn an otherwise mundane fight, into an actually interesting challenge.