If for an event you refer to something like the Reddit API fiasco then I wonder how many people joined here not because of Reddit, but because looking for social news aggregators.
Maybe some folks come from Mastodon but before Mastodon for me the Fediverse (indeed I just thought it was a selfhosted Twitter and nothing else) was non existent, even when I knew about Lemmy (on Reddit) I didn’t relate it with Mastodon.
I feel my smaller communities aren’t as active as I would like, I suppose the best way to fix this is that we all lurk less and contribute more, that and share fun stuff from here to acquaintances, even through other social media.