Some nether brick blocks make stone sounds

Many blocks made out of nether bricks make stone sounds when walking on them. Here are the ones:

 

Nether brick wall

Red nether brick wall

Nether brick slab

Red nether brick slab

Chiseled nether bricks

Cracked nether bricks

 

Here's a video demonstrating this: https://imgur.com/a/GHJjwXY