I do not think it is an uncommon story that many Buddhists develop their spiritual leanings from their grandparents. The grandparent/grandchild bond is a special one – grandparents are wizened with knowledge without the day-to-day responsibilities of child-rearing, which seems like just the right combination to imbue an appreciation of peace and a proclivity to contentedness.
I also see grandparents as muddling that already terrible “heritage Buddhist” definition – where children grow up encountering the Dharma from their grandparents even through their own parents had rejected that very series of influences.
I am not part of that muddled category as neither my parents nor my grandparents are Buddhist. Still, I would not have ended up a Buddhist without the opportunity to know my grandparents. They taught me generosity, always being willing to give what they had simply for the reason that it was there to give. I learned patience, temperance, and that doing what is right for your family requires doing what is right by your family.
That being said, I only terrifiedly came out about my wacky religion to my grandparents this last year.