It looks like they may have tweeted something about the elonjet account that still exists on mastodon, and were suspended under the new version / enforcement of Twitter's doxxing rules.

How many layers of soft links does it take before they can't detect you? If you linked to a Bloomberg article that linked to an elonjet, would that run afoul?

right? Does linking to reddit qualify since there's a subreddit for elonjet as well?

Confirmed. The last snapshot in the Wayback Machine shows that they tweeted a link to @ElonJet on Mastodon before being suspended: http://web.archive.org/web/20221215173935/https://twitter.co...

Part of me wonders if this was an intentional move on Mastodon’s part to make it look like Elon is silencing competitors.

This is increasingly absurd, but I see Twitter has also banned the official ADS-B account and antifascist website It's Going Down (which is mostly polemic op-eds and reports about political demonstrations in the US and Europe, and theoretically well within Twitter's TOS).