Looking at the source I don't think that's true -- it's using GitHub specific APIs to read/write files. It's not standard git so any remote wouldn't work, and the mechanics are more akin to a key-value store than git really.
Not to say you couldn't add a generic git protocol to this, just that that's not being done here.
Not to say you couldn't add a generic git protocol to this, just that that's not being done here.