Current Hardcore World which is 250 days right now has parts of chunks from my old Hardcore

On the late November 2021, I created a new, fresh hardcore as I took a break from Minecraft because on the late April 2021, I died on my 600 day Hardcore. One day on early January 2022, I played my hardcore which was at around 150 days at that time, and I chose to explore out of my base with an elytra. As I flew back home, I spotted something extremely strange, I saw a dug up pit of sand I never touched on that world. Then it hit me, somehow this dug up pit of sand in the desert biome is the same pit that I dup up in my old, 8 months ago, 600 day hardcore. I never touched that hardcore in those 8 months nor I altered my current hardcore to cheat. I created the new hardcore world fresh. I cannot explain how this has happened. Then all of a sudden, I also spot the same sand hill which was near the dup up sand from my old hardcore world in my new one. I do not know how this happened. I do not know if this was Minecraft's chunk loading for new world messed up, I do not know!

What is even stranger that when I did /seed in my current hardcore world and used it to create a creative world to see if this happens to it as well, when I wrote the coordinates from the sand pit and teleported, there was not even a desert biome. It was just an ocean biome.

I do not know and need answers.