That sword in stone thing is actually a prop from a medieval play about a legendary blacksmith.
Dude was so good at blacksmithing he could coax the ore out of rock and form it into a sword without forge or tools... or so the legend went at the time.
Or it is a practical joke created by time traveling ancient aliens. They went back in time and placed the sword into wet sediment knowing that it’d harden into rock. They do that sort of thing a lot, you know.