Since Twitter supports OExchange auto-discovery (see http://twitter.com/.well-known/host-meta), I consider it very likely that this is indeed intended as an OExchange endpoint. This standardized OExchange endpoint translates the request into a Twitter-specific Tweet Intent request. This makes perfect sense, but there’s just a flaw in the implementation as I described above.
Websites who want a specific Twitter sharing feature, can integrate Tweet Intents into their website, while websites who want to support a generic sharing function that works with any social network, can use the OExchange mechanism.
