It was designed as a security feature but it's been coopted to block competitors (or anyone else the CEO takes a personal disliking to). Therefore calling it an "anti-Mastadon" filter is accurate in this context, no matter the specifics of how that filter is currently implemented.

> 1. It's not an "anti-Mastadon" filter. It's a security feature of twitter's URL shortener for preventing spammers, malware spreaders, etc from propagating links to their stuff both on anb off twitter.

They've repurposed an existing Twitter tool (what else could they do, with nobody left to implement new tools?) to block Mastodon, but that's an active move to try and block Mastodon nonetheless.

Do you have any evidence for 1) ?