Grandpa lore is basically like dad lore. Its when they tell you the stuff they did and what they've experienced in their teens/early adult life. Probably before meeting the mother/father of your parent. Cool shit
Heika: I had a dream last night that I was caught by the cops with my friends on the river in the middle of the night in the 70s
Mal: Man that's Grandpa lore
Grandpa Lore: Another step above Dad lore. Stories that are told to grandkids but not your children. Stories that are unhinged about your life before or after your kids are born.
One day at the lake with the family
Grandson: Pop Pop can you tell me a story
Pop Pop: Well kiddo this one time I smoked a joint before your dad came home from school and I was so high that I left him outside to play with the other kids while I ate all of his fruit snacks and watched Spongebob. and that's why kiddo, drugs are bad.
Dad: *internal thoughts* "That asshole did eat my goddamn fruit snacks."
Grandson: wow that's some grandpa lore.