I don't think anyone other than druids/rangers can cast plant controlling spells so maybe the druid was mind controlled to perform the act at insight park?
It is good to take the possibility of mind control into account. It is quite possible that the urchin was mind controlled too, during our second encounter with him. But on the topic of plant control: if magic was involved, the only applicable spell that I could find is Plant Growth, and the description says bards can cast it too.
