Well, without more context, it's difficult to say exactly. Maybe it's a story where the grandma of one of the friends did something really heroic or kind. For example, she might have helped the community during a tough time, like a war or a natural disaster. Or perhaps it's a story about her cooking and how she used to make the most delicious meals for her family and friends.
I'm not sure specifically as I don't know which 'friends grandma story' you are referring to. It could be about all kinds of things like her adventures when she was young, how she met her husband, or some family traditions she passed on to her family and friends.
Since I don't have more details, I can only guess. It could be that the 'friends grandma story' is about the grandma's wisdom. She could have given great advice to her grandchildren and their friends. For instance, she might have told them how to deal with difficulties in life, like handling school problems or relationship issues. It could also be a story full of her memories from a different era, like how she grew up in a different cultural environment and what she learned from that.