Violet Fungus Tendril not classified as a plant

[djspectre]

I ran into 3 Violet Fungus Tendrils in the sewers and despite having a description that describes a plant creature, my sword which gains +2 magical damage vs. plants, didn't trigger the magical damage.

My belief is that the creature is not classified as a plant OR that the weapon's description doesn't match the properties of the weapon, meaning the weapon wasn't actually granted the +2 Magical damage vs plants property.