I’m thinking the guy at the gym may have been easing his former tormentor's guilt during the apology. Even if he said ~ “your bullying made me better”, I question if he even believes that as I seriously doubt bullying is something that helps men become better men, though there are a few life coaches that enjoy selling that storyline. I was picked on viciously in middle school and I’m still waiting for my life lesson.
On that story though, I had such a similar experience, from the reverse experience. Men bumping into their childhood bullies in adulthood and realizing their former target is much bigger is actually really common.