Warped forest over nether roof/ Able to get onto rood

I went to the nether for the first time to explore, (Good job BTW,) anyways, I went to the nether roof and explored for a while, I then stumbled across a Warped forest over the nether's roof. It was about 20 trees and a couple bits of the new grass. I checked underneath the grass and it was easily accessible to the regular nether.

What I expected to happen was...:
I expected there would be no biome on top of the roof. 

What actually happened was...:
There were trees and a few patches of grass, underneath them even more and it lead to the underworld.

Steps to Reproduce:
1. Go onto the nether roof
2. Search around for a bit

3. Break underneath the trees

4. Easily accessible to the underworld.