"PartnerNet is the name of the developers-only alternative Xbox Live network used by developers to beta test game content downloads, and games developed for Xbox Live Arcade. PartnerNet runs on Xbox 360 debug kits, which are used both by developers and by the gaming press."
That's true, JSR did release on xbla. I google searched Shenmue HD Partnernet and found that original rumor from 2010 or so concerning Shenmue 2 HD files up on that service. Though, nothing on shenmue ever materialized. The ops wording on this seems unusual plus he is saying that these files on partnernet now are related to Shenmue 1 and not Shenmue 2 as the original rumor alluded to. I don't fully understand how this service functions and what exactly the OP has indicated is uploading. Hopefully he steps in to shed more light on this.
I wonder if some partnernet files had been leaked somehow. Maybe it would result in a playable alpha for x360 but that wouldn't help the cause for any new shenmue material...
So if the files exist, that means a playable HD Shenmue exists for the Xbox 360? So a dev has completed the work and the decision lies with Microsoft wether or not to release it?