Cool, that likely means that something in your community got reposted by users on Mastodon. Because Mastodon is federated, the link preview crawlers will have different user agents. Both because the instances will be on different Mastodon versions and because it looks like Mastodon includes the URL of the community as part of the user agent.
Agreed. It could also be neat to group the user agents, so that you can see Mastodon link preview totals, Facebook onebox totals, Discourse onebox totals (from other communities) and so on.