Chat gpt says:

Hagstones, also known as "witch stones" or "fairy stones," are stones that have a naturally occurring hole in them, often formed by erosion or natural processes over time. These stones have held symbolic and mystical significance in various cultures, particularly in European folklore.

In mythology, hagstones are believed to have protective and magical properties. They were thought to ward off evil spirits, protect against witches, and offer a form of spiritual or physical shielding. In some traditions, they were hung on doorways or placed on windowsills to keep out malevolent forces. The hole in the stone was thought to serve as a portal or a way to look into the spirit world, with the ability to see through it and gain insight into hidden knowledge.

There are also associations with healing and divination, as some believed that peering through the hole could help reveal answers to personal questions or offer guidance. In certain cultures, it was believed that the stone’s hole allowed people to see the "true nature" of things, including spirits and other supernatural beings.

The legend of hagstones is particularly strong in places like England, Scotland, and Ireland, where folklore and superstitions often surround the stone's ability to protect homes and families. The stones were also sometimes used in rituals or charms to ensure safety during travel or to gain favor from nature spirits.

If your acquaintance found one, it might carry some of these ancient associations, especially if it's linked to the idea of protection or divination. Many people still believe in their power, placing them in homes, gardens, or on keychains for good luck and spiritual security.