A reason for the letters being in the cave was not shown.
Debated. How the writing got there is not settled.
In Kateřinská Cave, in the Czech Republic, pieces of stone were found with cuneiform letters. Cuneiform is writing from ancient Mesopotamia. One piece is part of a carving that looks like people walking in a line. The page does not give an age.
The page says it is still unknown how this writing reached a cave in Central Europe. It mentions travellers and trade, and says another answer is possible too.
https://www.ancient-origins.net/news-history-archaeology/cuneiform-oopart-czech-republic-00102398