100 years doesn't require a game of telephone with 20 people. It requires maybe 2 or 3. And for a event known to a whole town, you have multiple independent narrators which can help stabilize information.

My family has far more trivial information passed down orally that is way older than 100 years.

Mine doesn't. I know just a handful of things about my great grandparents. Things I do know about my family history didn't come from oral traditions but rather records placing my ancestors in places.

Even from what I know of my parents, I'm sure I've forgotten or misremembered a bunch of stories that they've told me about their lives. I couldn't reliably retell more than a handful of stories.