random piles of mossy cobblestone spwan around the world in the seed of forest glade in the seed picker

That's not a bug 🐞. It's a feature of the biome you are in. 

See https://minecraft.gamepedia.com/Giant_Tree_Taiga

You can see the boulders in the first pic of this biome tweeted by Jeb.

No it's a bug I am sure because the boulders spawns in other biomes too very far away I've made a new world and detected every place where they spawn and some spawned in a cave of mountains . I got biome data by using chunk base. 

Mossy cobblestone in a cave is probably part of a dungeon wall. Mossy cobblestone also occurs in the walls of village buildings.

the mossy cobblestone was inside a cave out in the open no spawner in sight and a village was about a 100 - 150 blocks away and the world I searched it in was created in 1.16.64 beta and the place wasn't generated at that time. When it was generated in 1.16.66 beta

I tried the same seed (in 1.14.60) and one of the places where mossy cobblestone was, wasn't there I've posted another screenshot of the place (I am not lying) I made two worlds and one had mossy cobblestone there and other didn't. I accidentally deleted the world where mossy cobblestone was there as I was deleting my old flat worlds where I did some glitch testing seen from videos of silentwisperer

@@unknown perhaps there was a generation glitch that only happened in the one world? I had someone load that cave 1.16.0.67 and there is no boulder in it. Here is the cave in 1.14.60 and 1.16.0.67 beta side-by-side. You can see that the generation of block types is a bit different, but it's the same cave an no boulder.

I think it happened to my world as one had a boulder and other didn't and a great taiga biome is next to that cave 

there is a bug in 1.16.67 that hasn't been fixed yet but many people have reported mcpe-79736 it says it is resolved but it isn't 

“Resolved” means that the ticket is resolved, not that the reported problem is resolved. The ticket you mention has a resolution of “duplicate,” which means that the reported problem is being tracked on another ticket.