Stone and Cobblestone can naturally generate below Y 0 if Water touches Lava.

While I was mining, I found random blocks of Stone and Cobblestone among Deepslate where water and Lava touch each other.

What went wrong: Stone shouldn't be below Y 0 without the action of player.

Expected result: when Lava touches Water, Deepslate would generate.

How to Fix: Make it that if Lava touches Water below Y 0, Deepslate would generate and if Water touches Lava below Y 0, Cobbled Deepslate would generate.